Preamble

Correlation Between Low Iron Status and Clinical Characteristics of Patients with Colorectal Adenocarcinoma

Abstract

Objective: To investigate the correlation between low iron status and the clinical characteristics of patients diagnosed with colorectal adenocarcinoma.

Methods: A retrospective analysis was conducted on clinical data from patients with pathologically confirmed colorectal adenocarcinoma. Patients were categorized into low iron and normal iron groups based on serum ferritin and transferrin saturation levels. Statistical methods were employed to compare demographic data, tumor location, pathological grading, clinical staging, and laboratory parameters between the two groups.

Results: The study found that patients in the low iron group exhibited significant differences in tumor site (with a higher prevalence in the right colon) and advanced clinical stages compared to the normal iron group. Furthermore, low iron status was frequently associated with lower hemoglobin levels and specific inflammatory markers.

Conclusion: Low iron status is closely related to the clinical progression and anatomical location of colorectal adenocarcinoma. Monitoring iron metabolism parameters may provide valuable insights for the clinical assessment and management of these patients.

Introduction

Colorectal cancer (CRC) remains one of the most prevalent malignancies worldwide, with adenocarcinoma being its most common histological subtype. In recent years, the relationship between systemic metabolic status and tumor progression has gained increasing attention. Among these factors, iron—an essential trace element for DNA synthesis and cellular proliferation—plays a dual role in oncology. While iron is necessary for normal physiological functions, dysregulation of iron metabolism is frequently observed in cancer patients.

Low iron status, often manifesting as iron deficiency with or without anemia, is a common systemic complication in colorectal adenocarcinoma. This is typically attributed to chronic occult bleeding from the tumor surface, nutritional deficiencies, or the systemic inflammatory response which sequesters iron. Understanding the correlation between iron levels and clinical characteristics is vital for improving diagnostic accuracy and optimizing therapeutic strategies. This study aims to analyze the clinical data of patients with colorectal adenocarcinoma to clarify how low iron status relates to tumor behavior and patient prognosis.

Materials and Methods

1.1 Study Population

We retrospectively collected data from patients diagnosed with colorectal adenocarcinoma at our institution. Inclusion criteria were: (1) histopathological confirmation of colorectal adenocarcinoma; (2) complete medical records including iron metabolism panels (serum ferritin, serum iron, and total iron-binding capacity); and (3) no prior history of iron supplementation or blood transfusion within three months before diagnosis. Exclusion criteria included patients with other concurrent primary malignancies or severe systemic inflammatory diseases unrelated to the tumor.

1.611137 School of Medicine and Life Sciences, Chengdu University of Traditional Chinese Medicine, Chengdu, Sichuan Province, China

Department of Colorectal Surgery, Sichuan Cancer Hospital, Chengdu, Sichuan Province, China

Background

Colorectal cancer is the second most prevalent malignant tumor globally. Research indicates that iron metabolism is involved in multiple stages of tumor progression, including tumor cell proliferation and the regulation of the immune microenvironment. Clinically, patients with colorectal cancer frequently exhibit abnormal serum iron status, with low serum iron levels being the most common manifestation. Investigating the correlation between a low-iron state and colorectal cancer is of significant importance for the development of individualized treatment strategies for this disease.

The objective of this study is to comprehensively and systematically explore the relationship between the internal low-iron environment in patients with colorectal cancer and various clinical characteristics.

Methods

This study is a retrospective cohort study based on a single-center registry. We consecutively enrolled 712 patients with postoperatively pathologically confirmed colorectal adenocarcinoma at Sichuan Cancer Hospital between January 2017 and June 2023. We collected data on serum iron, transferrin saturation, and various clinical characteristics. Based on preoperative serum iron levels, patients were divided into a low iron status group (low iron group, $n=363$) and a control group with normal iron status ($n=349$).

To minimize potential bias, Propensity Score Matching (PSM) was employed to match patients in a 1:1 ratio with a caliper set at 0.2. This resulted in a final matched sample of 698 cases (349 cases each in the low iron and control groups). Univariate analysis and multivariate logistic regression analysis were then utilized to investigate the correlation between low iron status and various clinical characteristics.

Results

Among the 712 patients included in the study, 363 (50.98%) were found to be in a state of internal iron deficiency. Prior to Propensity Score Matching (PSM), significant statistical differences were observed between the control group and the iron-deficient group regarding American Society of Anesthesiologists (ASA) physical status classification, the proportion of cancerous obstructions, and the prevalence of anemia ($P < 0.05$). Following PSM, these differences in ASA classification, cancerous obstruction rates, and anemia prevalence remained statistically significant ($P < 0.05$).

In the post-PSM iron-deficient group, white blood cell count (WBC), C-reactive protein (CRP), plateletcrit (PCT), and carcinoembryonic antigen (CEA) expression levels were significantly higher than those in the control group. Conversely, lymphocyte count (LY), albumin (ALB), and serum total cholesterol (TC) levels were significantly lower in the iron-deficient group ($P < 0.05$). Furthermore, there were statistically significant differences between the two groups regarding tumor location, Union for International Cancer Control (UICC) TNM stage, pathological type, degree of differentiation, mismatch repair (MMR) status, microsatellite stability status, nerve and vascular invasion, rates of liver and lung metastasis, and maximum tumor diameter ($P < 0.05$).

After utilizing PSM to control for baseline confounding factors, multivariate logistic regression analysis was performed. When anemia was excluded as an independent predictive variable, the analysis revealed that tumor location (rectum: $OR = 0.410$, $95\% CI = 0.25\text{--}0.67$, $P < 0.01$), UICC stage IV ($OR = 3.50$, $95\% CI = 1.65\text{--}7.82$, $P < 0.01$), vascular invasion ($OR = 1.63$, $95\% CI = 1.01\text{--}2.63$, $P = 0.04$), tumor diameter ($OR = 1.16$, $95\% CI = 1.03\text{--}1.30$, $P < 0.01$), ALB ($OR = 0.90$, $95\% CI = 0.85\text{--}0.95$, $P < 0.01$), PCT ($OR = 1.12$, $95\% CI = 1.08\text{--}1.15$, $P < 0.01$), and LY ($OR = 0.51$, $95\% CI = 0.35\text{--}0.72$, $P < 0.01$) were independent factors influencing the iron-deficient state in patients with colorectal adenocarcinoma.

When anemia was included in the multivariate logistic regression model, anemia itself emerged as a strong independent factor for iron deficiency ($OR = 7.03$, $95\% CI = 4.40\text{--}11.25$, $P < 0.01$). Under this model, tumor location was no longer an independent factor; however, tumor diameter, UICC stage IV, vascular invasion, and peripheral blood markers (LY, PCT, and ALB) remained independently associated with the iron-deficient state in colorectal adenocarcinoma patients ($P < 0.05$).

Conclusion

Correlation Analysis between Low Iron Status and Clinical Characteristics of Colorectal Cancer Patients

Abstract: The internal iron status of patients with colorectal adenocarcinoma is closely related to tumor invasiveness (including clinical stage, lymphovascular invasion, and maximum tumor diameter) as well as inflammatory markers. Factors such as a rectal primary site and higher levels of albumin (ALB) and lymphocytes (LY) serve as protective factors against low iron status in patients with colorectal adenocarcinoma. Conversely, anemia, UICC Stage IV, lymphovascular invasion, larger tumor diameter, and procalcitonin (PCT) levels are identified as risk factors for low iron status.

Keywords: Colorectal neoplasms; Colorectal adenocarcinoma; Tumor microenvironment; Internal iron status; Low iron status

CLC Number: R 735.34
Document Code: A

Introduction

Colorectal adenocarcinoma remains a significant global health burden, and recent research has increasingly focused on the role of the tumor microenvironment and systemic metabolic states in disease progression. Among these factors, iron metabolism plays a critical role in both cellular proliferation and immune function. This study aims to analyze the correlation between low iron status and various clinical characteristics in patients diagnosed with colorectal adenocarcinoma.

Results and Discussion

Our analysis demonstrates that the internal iron status of patients with colorectal adenocarcinoma is significantly associated with markers of tumor invasiveness and systemic inflammation. Specifically, we observed that iron deficiency or low iron status is more prevalent in patients exhibiting advanced disease characteristics.

1. Tumor Invasiveness and Iron Status

The data indicate a strong correlation between low iron status and several key indicators of tumor progression. Patients with UICC Stage IV disease, lymphovascular invasion, and larger maximum tumor diameters were significantly more likely to present with low iron levels. These findings suggest that as the tumor burden increases and the disease becomes more invasive, the systemic iron reserves are progressively depleted, likely due to a combination of chronic blood loss, nutritional deficiencies, and the systemic inflammatory response.

2. Inflammatory Markers and Protective Factors

Inflammation plays a dual role in colorectal cancer. Our study found that elevated procalcitonin (PCT) levels are a risk factor for low iron status, reflecting the "anemia of chronic disease" or "anemia of inflammation" often seen in cancer patients. In contrast, higher levels of albumin (ALB) and lymphocytes (LY) were identified as protective factors. These markers are generally indicative of better nutritional status and robust immune function, respectively, which may help maintain iron homeostasis.

3. Clinical Risk Factors

The primary site of the tumor also appears to influence iron status. Patients with rectal cancer tended to have higher iron levels compared to those with tumors in other parts of the colon, suggesting that the anatomical location may influence the severity of iron depletion. Furthermore, clinical anemia and

Chinese General Practice, 2025. [Epub ahead of print].

Editorial Office of Chinese General Practice. This is an open access article under the CC BY-NC-ND 4.0 license.

Chinese General Practice Corresponding author: Hu Hai, Associate Chief Physician.

Background

Colorectal cancer (CRC) is the second most common malignant tumor in terms of incidence worldwide. Studies have shown that iron metabolism is involved in multiple aspects of tumor progression, such as tumor cell proliferation and immune microenvironment regulation. Clinically, most CRC patients are accompanied by abnormal serum iron status, among which low serum iron levels are more common. Exploring the correlation between low iron status and colorectal cancer is of great significance for the individualized treatment of colorectal cancer.

Objective: This study aims to comprehensively and systematically investigate the relationship between the internal environment low iron status and various clinical characteristics in patients with colorectal adenocarcinoma.

Methods

Based on a single-center registered retrospective cohort study, 712 patients who were pathologically diagnosed with colorectal adenocarcinoma after surgery at Sichuan Cancer Hospital from January 2017 to June 2023 were consecutively included as research subjects. Indicators including serum iron, transferrin saturation, and various clinical characteristics were collected. Patients were divided into the low iron status group (low iron group, $n=363$) and the control group with normal iron status ($n=349$) according to the preoperative serum iron expression level. Propensity score matching (PSM) was used for 1:1 matching of patients, with a caliper set at 0.2. Finally, 698 matched samples were included (349 cases in both the low iron group and the control group). Univariate analysis and multivariate Logistic regression analysis were used to explore the correlation between low iron status and clinical characteristics.

Results

Among the 712 patients, 363 cases (50.98%) had low iron status in the internal environment. Before PSM matching, there were statistically significant differences between the control group and the low iron group in the American Society of Anesthesiologists (ASA) classification, the proportion of cancer obstruction, and the proportion of anemia ($P < 0.05$); after PSM matching, the differences in ASA classification, the proportion of cancer obstruction, and the proportion of anemia between the two groups were still statistically significant ($P < 0.05$). After PSM matching, the expression levels of white blood cell count (WBC), C-reactive protein (CRP), plateletcrit (PCT), and carcinoembryonic antigen (CEA) in the low iron status group were higher than those in the control group, while the levels of lymphocyte count (LY), albumin (ALB), and serum total cholesterol (TC) were lower than those in the control group ($P < 0.05$). There were statistically significant differences between the two groups in tumor location, International Union Against Cancer (UICC) TNM stage, pathological type, degree of differentiation, mismatch repair (MMR) expression status, microsatellite stability status, nerve and vascular invasion, liver and lung metastasis rates, and tumor length ($P < 0.05$). After controlling for baseline confounding factors using PSM, anemia was separated as an independent predictive variable for multivariate Logistic regression analysis. The results showed that when anemia was not included, tumor location (rectum, $OR = 0.410$, $95\% CI = 0.25\text{--}0.67$, $P < 0.01$), UICC stage IV ($OR = 3.50$, $95\% CI = 1.65\text{--}7.82$, $P < 0.01$), vascular invasion ($OR = 1.63$, $95\% CI = 1.01\text{--}2.63$, $P = 0.04$), tumor length ($OR = 1.16$, $95\% CI = 1.03\text{--}1.30$, $P < 0.01$), ALB ($OR = 0.90$, $95\% CI = 0.85\text{--}0.95$, $P < 0.01$), PCT ($OR = 1.12$, $95\% CI = 1.08\text{--}1.15$, $P < 0.01$), and LY ($OR = 0.51$, $95\% CI = 0.35\text{--}0.72$, $P < 0.01$) were independent influencing factors for low iron status in patients with colorectal adenocarcinoma. When anemia was included in the multivariate Logistic regression analysis, anemia ($OR = 7.03$, $95\% CI = 4.40\text{--}11.25$, $P < 0.01$) became an independent influencing factor for low iron status, while tumor location was no longer an independent influencing factor. The remaining factors, including tumor length, UICC stage IV, vascular invasion, and peripheral blood LY, PCT, and ALB, were still independent factors associated with low iron status in patients with colorectal adenocarcinoma ($P < 0.05$).

Conclusion

The internal environment iron status of patients with colorectal adenocarcinoma is closely associated with tumor invasiveness (including tumor stage, neurovascular invasion, and tumor length) as well as inflammatory indicators. Rectal tumor location, along with higher levels of albumin (ALB) and lymphocyte count (LY), are protective factors against low iron status in patients with colorectal adenocarcinoma. In contrast, anemia, UICC stage IV, vascular invasion, longer tumor length, and higher plateletcrit (PCT) are risk factors for low iron status. As the second leading cause of cancer death worldwide, colorectal cancer (CRC) research remains a primary focus in the global medical field. According to statistics, the incidence and mortality rates of CRC in China rank second and fifth among all malignant tumors, respectively, and both the number of cases and deaths continue to grow annually. However, the exact causes of its occurrence and progression are not yet fully understood. In recent years, with deepening research into the mechanisms of tumorigenesis and progression, increasing attention has been paid to the tumor microenvironment and the overall metabolic state of the body.

During the occurrence and development of colorectal cancer, iron ions are considered one of the key regulatory factors in tumor progression; either excess or deficiency can lead to different pathological conditions. As an essential trace element for the human body, iron participates in vital processes such as oxygen transport, cellular respiration, and immune regulation. The mechanism of ferroptosis in colorectal cancer, which is directly related to the iron status of the internal environment, is also a current research hotspot \cite{2-3}. Patients with colorectal cancer often present with abnormal iron status. Multiple studies have shown that excessive intestinal iron increases intracellular oxidative stress and lipid peroxidation, which can promote oncogene activation by affecting protein modification and causing DNA damage, while also providing iron for cancer cell proliferation and promoting tumor development \cite{4-5}. However, statistics indicate that serum iron levels in colorectal cancer patients are generally low, and the relationship between a low-iron internal environment and colorectal cancer has not been fully evaluated.

Currently, research on the relationship between colorectal cancer and low iron status has certain limitations. Existing studies primarily focus on the association between decreased transferrin or ferritin and specific characteristics of colorectal cancer, often neglecting a comprehensive analysis of the relationship between serum iron status/deficiency and various clinicopathological factors. Furthermore, there are deficiencies regarding sample size, research methodology, and the interpretation of results \cite{7-8}. Serum iron is a direct reflection of the bioavailability of iron within the internal environment, and its levels are crucial for maintaining basic cellular physiological functions. Therefore, this study aims to detect preoperative serum iron and related indicators in patients with colorectal adenocarcinoma. By combining these with various clinicopathological factors for correlation analysis, we hope to provide a reference for exploring comprehensive treatment models for colorectal adenocarcinoma patients and offer comprehensive, systematic research results to further understand the relationship between colorectal adenocarcinoma and a low-iron internal environment.

1.1 Study Population

This study is a retrospective cohort study based on a single-center registry. A total of 712 patients who were diagnosed with colorectal cancer and underwent surgery at the Sichuan Cancer Hospital between January 2017 and June 2023 were consecutively enrolled. The inclusion criteria were as follows: (1) patients who underwent surgical treatment at Sichuan Cancer Hospital following diagnosis and were pathologically confirmed to have colorectal adenocarcinoma; (2) patients who received a single surgical treatment protocol for colorectal cancer; (3) patients with at least one recorded preoperative blood test at the hospital; and (4) patients with complete medical records. The exclusion criteria were: (1) patients who underwent treatments or experienced events significantly affecting observational indicators within the past six months (such as blood transfusions, iron therapy, chemotherapy, traumatic blood loss, or severe infection); and (2) patients who underwent endoscopic surgery or received neoadjuvant therapy.

This study was approved by the Medical Ethics Committee of Sichuan Cancer Hospital (Approval No.: SCCHEC-02-2024-069), and informed consent was obtained from all patients and their families.

1.2.1 Patient Grouping

Participants were divided into a low iron status group ($n=363$) and a control group with normal iron status ($n=349$). The low iron group was defined as follows: males with serum iron $\le 10.6$ µmol/L and females with serum iron $\le 7.8$ µmol/L, or functional iron deficiency characterized by a transferrin saturation (TSAT) $\le 20\%$ \cite{9-10}. The control group consisted of males with serum iron $> 10.6$ µmol/L and females with serum iron $> 7.8$ µmol/L, both with a TSAT $> 20\%$.

1.2.2 Observation Indicators

Smoking status, American Society of Anesthesiologists (ASA) physical status classification, postoperative pathological results, mismatch repair (MMR) expression, and peripheral blood parameters were recorded. These parameters included hemoglobin (Hb), serum iron (SI), transferrin saturation (TSAT), white blood cell (WBC) count, total protein (TP), serum albumin (ALB), lymphocyte (LY) count, C-reactive protein (CRP), total cholesterol (TC), triglycerides (TG), plateletcrit (PCT), and carcinoembryonic antigen (CEA).

Colorectal cancer staging was performed according to the TNM staging criteria published by the Union for International Cancer Control (UICC).

The study utilized pTNM staging from postoperative pathological reports and M-stage at the time of evaluation. For Hb, SI, and TSAT, the minimum values recorded between one week after the diagnosis of colorectal adenocarcinoma and the time of surgery were used. For serum proteins, CRP, WBC, LY, PCT, and tumor markers, the final laboratory test results prior to surgery were selected. Selecting the minimum values for iron-related parameters serves to minimize the risk of unrecorded iron supplementation acting as a confounding factor. Statistical analysis was performed using SPSS 26.0 software.

Quantitative data following a normal distribution are expressed as ($\bar{x} \pm s$), and comparisons between two groups were performed using the independent samples $t$-test. Categorical data are expressed as relative numbers (percentages), and comparisons were conducted using Chi-square tests.

2 Results and Analysis

Python (3.12.1) was used to analyze the tumor pathological results and clinical data.

1.1 Baseline Characteristics and Propensity Score Matching

In this study, linear regression and heatmap analysis were conducted to evaluate serum iron levels. Initially, univariate analysis was performed on the 712 collected patient cases. To control for the influence of baseline confounding factors, propensity score matching (PSM) was employed to balance the patient cohorts.

[TABLE:1]

1.2 Linear Regression Analysis of Serum Iron Levels

Following the matching process, we utilized linear regression models to explore the associations between serum iron levels and various clinical parameters. This approach allowed for a quantitative assessment of how specific biomarkers and demographic variables correlate with iron homeostasis in the target population. The regression coefficients ($\beta$) were calculated to determine the strength and direction of these relationships, ensuring that potential confounders identified in the univariate stage were adequately addressed.

1.3 Heatmap Visualization of Clinical Correlations

To further visualize the complex interactions between serum iron and other biochemical markers, a heatmap analysis was performed. This graphical representation facilitates the identification of clusters and patterns within the dataset that may not be immediately apparent through standard tabular data. By integrating the results of the PSM-adjusted cohort, the heatmap provides a comprehensive overview of the metabolic landscape, highlighting significant correlations (e.g., $p < 0.05$) across the 712 patient samples.

[FIGURE:1]

1 Matching

Factors that demonstrated statistically significant differences in the univariate analysis were included in the model, with the caliper set to 0.2. Intergroup differences were reassessed following the matching process. Ultimately, a matched sample of 698 cases (349 cases each in the low-iron group and the control group) was included in the multivariable logistic regression analysis.

An evaluation of missing data within the dataset revealed that cases with complete data accounted for 96.68% of the total. Multiple imputation models were employed to address missing values using five complete variables alongside the outcome variable (iron status). The accuracy of the imputation was subsequently verified using the Monte Carlo error analysis method. A p-value of less than 0.05 was considered to indicate a statistically significant difference.

2.1 General Patient Information

Among the 712 cases included in this study, 363 (50.98%) were classified as having low iron status. Consequently, the cohort was divided into a low iron group ($n=363$) and a control group ($n=349$). Prior to Propensity Score Matching (PSM), statistically significant differences were observed between the control and low iron groups regarding ASA physical status, the proportion of cancerous obstruction, and the prevalence of anemia ($P < 0.05$). However, no statistically significant differences were found between the two groups in terms of sex, age, smoking status, BMI, or the prevalence of hypertension and diabetes ($P > 0.05$). Following PSM, the differences in ASA status, cancerous obstruction, and anemia remained statistically significant ($P < 0.05$), as detailed in [TABLE:1].

Comparison of Blood Indicators Between the Two Groups After Matching

After matching, the expression levels of white blood cell count (WBC), C-reactive protein (CRP), procalcitonin (PCT), and carcinoembryonic antigen (CEA) were significantly higher in the low iron status group compared to the control group. Conversely, the levels of lymphocytes (LY), albumin (ALB), and total cholesterol (TC) were lower in the low iron group than in the control group, with these differences being statistically significant.

[TABLE:1] Comparison of baseline characteristics between control and low-iron groups before and after matching.

3 Results

For ASA classification, the distribution was as follows: 25 (7.16%) vs 27 (7.44%) before matching, and 25 (7.16%) vs 26 (7.45%) after matching. Note: ASA = American Society of Anesthesiologists physical status classification. There was a statistically significant difference ($P < 0.05$); however, there was no statistically significant difference when comparing TP and TG between the two groups ($P > 0.05$), as shown in [TABLE:2].

[TABLE:2] Comparison of laboratory parameters between groups after PSM.

Variable (Unit) Control Group Low Iron Group $t$ $P$ WBC ($\times 10^9/L$) $5.76 \pm 1.59$ $6.16 \pm 2.18$ -2.83 <0.01 ALB ($g/L$) $41.51 \pm 3.76$ $39.23 \pm 4.27$ 7.54 <0.01 LY ($\times 10^9/L$) $1.60 \pm 0.68$ $1.45 \pm 0.51$ 3.29 <0.01 CRP ($mg/L$) $3.71 \pm 6.92$ $10.54 \pm 20.67$ -5.76 <0.01 TC ($mmol/L$) $4.73 \pm 0.96$ $4.42 \pm 0.91$ 4.50 <0.01 PCT ($\%$) $0.21 \pm 0.05$ $0.25 \pm 0.08$ -7.75 <0.01 CEA ($ng/mL$) $8.36 \pm 18.53$ $15.03 \pm 45.93$ -2.57 <0.01

Note: WBC = White Blood Cell count, TP = Total Protein, ALB = Albumin.

2.3 Comparison of Tumor Pathological Characteristics

There were statistically significant differences between the two groups regarding tumor location, UICC TNM stage, pathological type, degree of differentiation, MMR status, microsatellite stability status, nerve and vascular invasion, rates of liver and lung metastasis, and tumor longitudinal diameter ($P < 0.05$), as shown in [TABLE:3].

Since iron deficiency and the development of anemia follow a clear unidirectional causal progression \cite{11-12}, anemia was treated as an independent predictive variable and analyzed separately in the multivariate Logistic regression analysis of factors influencing low iron status. Variables that showed statistical significance in the univariate analysis after PSM matching were included as independent variables. These were assigned values as follows: tumor location (ascending colon = 1, transverse colon = 2, descending colon = 3, rectum = 4); UICC stage (Stage I = 1, Stage II = 2, Stage III = 3, Stage IV = 4); vascular invasion (absent = 1, present = 2); and quantitative data were assigned their measured values. Iron status served as the dependent variable (normal iron status = 1, low iron status = 2).

The results of the multivariate Logistic regression analysis indicated that tumor location (rectum), tumor longitudinal diameter, UICC Stage IV, vascular invasion, and peripheral blood levels of LY, PCT, and ALB were independent risk factors for low iron status in patients with colorectal adenocarcinoma ($P < 0.05$), as shown in [TABLE:4]. After including anemia in the multivariate Logistic regression analysis, anemia emerged as an independent factor influencing low iron status, while tumor location was no longer an independent factor. However, tumor longitudinal diameter, UICC Stage IV, vascular invasion, and peripheral blood LY, PCT, and ALB remained independently associated with low iron status in these patients ($P < 0.05$), as shown in [TABLE:5].

Heatmap analysis demonstrated a significant downward trend in serum iron levels corresponding to different tumor locations and the progression of clinical stages [FIGURE:1].

3 Discussion

Previous studies have suggested that iron deficiency in patients with colorectal cancer is caused by intraluminal tumor bleeding, malignancy-induced inflammation, or a combination of both; however, a definitive conclusion has yet to be reached \cite{6, 12-13}. Currently, the relationship between iron deficiency and the progression of colorectal cancer has been partially explained from biological and immunological perspectives. Tumor cell proliferation requires a substantial amount of nutrients, with iron being one of the essential elements. However, the mechanisms by which tumor cells acquire iron may be altered. On one hand, tumor cells may upregulate the expression of certain iron transport proteins to enhance their iron uptake capacity, leading to a relative reduction in available iron within the tumor microenvironment and resulting in a systemic state of low iron. On the other hand, tumor cells may induce an immune response that alters the distribution of iron within the body. For instance, macrophage polarization and changes in the Treg population can increase iron production and the export of iron to the tumor microenvironment, thereby leading to a decrease in iron levels within the body's internal environment \cite{14-15}. From the perspective of overall systemic metabolism, patients with colorectal cancer may experience iron metabolism disorders leading to a low iron state due to factors such as tumor consumption and insufficient nutritional intake.

This study focuses on patients with colorectal adenocarcinoma. After controlling for baseline confounding factors through Propensity Score Matching (PSM) and multivariate Logistic regression analysis, it was found that UICC stage IV, albumin (ALB), and procalcitonin (PCT) levels are independent influencing factors for a low iron state ($P < 0.05$).

Heatmap analysis results also indicate that the pathological stage of colorectal adenocarcinoma is an independent factor influencing the internal low iron state. Within the pathological staging, significant differences were observed in T-stage and M-stage between the low iron group and the control group. Multivariate Logistic regression analysis, which included anemia, verified that tumor location is an independent factor for a low iron state. Tubular adenocarcinomas of the ascending and transverse colon are more likely to bleed than those in the descending colon, sigmoid colon, and rectum, leading to greater iron loss and a more pronounced systemic inflammatory response \cite{11-12, 16}. This study found no significant relationship between lymph node metastasis and low iron status in colorectal adenocarcinoma; however, the internal low iron state was more prominent in patients with distant metastasis \cite{14, 17}. Additionally, lymphocyte (LY) counts in the low iron group were significantly lower than those in the control group, while the number of patients with vascular invasion and the mean PCT levels were higher than those in the normal group.

[FIGURE: Heatmap of serum iron level variations in relation to tumor location and Union for International Cancer Control (UICC) staging in patients]

The relationship between this low iron state and tumor aggressiveness may be related to the following factors: (1) Immunosuppression or immune induction formed by the low iron state within the tumor microenvironment promotes tumor progression. (2) The low iron state may alter the tumor microenvironment by affecting platelet function and PCT levels. On one hand, low iron affects normal platelet function, which may lead to abnormal coagulation states in the tumor microenvironment, promoting thrombosis and creating favorable conditions for the survival and metastasis of tumor cells. On the other hand, elevated PCT may alter the distribution and concentration of cytokines and growth factors in the tumor microenvironment, which in turn affects the proliferation, invasion, and metastatic capacity of tumor cells.

Simultaneously, tumor cells may affect the function and quantity of platelets by secreting certain substances, further regulating iron metabolism and platelet status within the tumor microenvironment to form a complex interaction network \cite{17-19}. (3) A low iron state may allow tumor cells to escape ferroptosis by limiting the supply of iron ions required for this process, thereby gaining a survival advantage. Conversely, the body may regulate iron metabolism through compensatory mechanisms to adapt to a low iron environment. These mechanisms may interfere with the expression and function of ferroptosis-related proteins, further affecting the ferroptosis process in tumor cells \cite{3, 14}. Changes in the expression of certain iron transport proteins may affect intracellular iron uptake and storage, thereby influencing sensitivity to ferroptosis. This abnormal regulation of ferroptosis may be associated with increased tumor aggressiveness and metastasis, providing favorable conditions for the progression of colorectal adenocarcinoma.

In this study, a close relationship was also observed between ALB and serum low iron status ($OR = 0.90$, $95\% CI = 0.85\text{--}0.95$, $P = 0.04$). In cases of iron deficiency, the body may reduce ALB synthesis to conserve energy and resources, which may lead to decreased blood ALB levels. Furthermore, iron can indirectly affect the synthesis and secretion of ALB by influencing the metabolic functions of the liver. Conversely, the level and functional state of ALB also affect iron metabolism. Low ALB levels may lead to reduced efficiency in iron transport and utilization, making iron more prone to accumulation or deficiency in the body. ALB can also influence iron transport and storage by regulating the activity of transferrin. Combined with previous research findings, it can be concluded that low iron is a factor in the deterioration of the systemic nutritional status of tumor patients.

In this study, inflammatory markers (WBC, LY, PCT) were significantly higher in the low iron group compared to the control group, which to some extent confirms that malignancy-induced inflammation leads to a low iron state in the body \cite{11, 13, 18}. There was no significant difference in gender between the two groups, which differs from previous studies; this discrepancy may be related to the physiological differences in baseline levels between genders used to define low iron status \cite{7-8, 21}. The association of low iron with poorer clinical manifestations and performance status was validated in univariate tests ($P < 0.05$). However, this association was not confirmed when using multivariate analysis.

Colorectal adenocarcinoma patients with deficient mismatch repair (including both low and high microsatellite instability) are more likely to be in a low iron state. The low iron state may be related to the degree of tumor cell differentiation; specifically, a lower degree of differentiation may lead to lower internal iron concentrations, which may relate to the previously discussed relationship between tumor aggressiveness and iron levels. Contrary to the predicted iron loss caused by ulcerative bleeding, there was no significant correlation between the pathological types of colorectal adenocarcinoma (medullary, scirrhous, protuberant, ulcerative) and the low iron state \cite{11, 13}. This study still has limitations: (1) The data originated from a single center, resulting in insufficient sample representativeness; (2) There was a high degree of patient selection bias.

This study confirms that the low iron state in patients with colorectal adenocarcinoma is not simply related to a single factor; rather, multiple clinical factors interact to influence the occurrence, development, and metastasis of the tumor. The results of this study suggest that, in terms of treatment, iron metabolism could be regulated to improve immune function and inhibit tumor invasion and metastasis, given the relationship between the internal low iron state and colorectal adenocarcinoma. For example, pharmacological interventions could regulate the activity of iron transport proteins, or appropriate iron supplementation could improve the patient's iron status while avoiding the negative effects of iron overload. Furthermore, iron status can be considered an important prognostic indicator. When evaluating patient prognosis, clinicians should consider the patient's iron status and factors related to iron metabolism to more accurately predict disease progression and the risk of recurrence.

Author Contributions: Luo Hao and Luo Yajun proposed the main research objectives and performed the conception and design of the study. Luo Hao was responsible for the implementation of the research, statistical processing, and writing the manuscript. Yang Yi performed data collection and organization, as well as the drawing and presentation of figures and tables. Hu Hai was responsible for quality control and review of the article, held overall responsibility for the manuscript, and provided supervision and management.

The authors declare no conflicts of interest.

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