Influence of iron on in vivo proliferation and lethality of L1210 cells

Expanding the spectrum of the hyperferritinemic syndrome, from pathogenic mechanisms to clinical observations, and therapeutic implications

From the introduction of hyperferritinemic syndrome concept, a growing body of evidence has suggested the role of ferritin as a pathogenic mediator and a relevant clinical feature in the management of patients with inflammatory diseases. From a pathogenic point of view, ferritin may directly stimulate the aberrant immune response by triggering the production of pro-inflammatory mediators in inducing a vicious pathogenic loop and contributing to the occurrence of cytokine storm syndrome. The latter has been recently defined as a clinical picture characterised by elevated circulating cytokine levels, acute systemic inflammatory symptoms, and secondary organ dysfunction beyond that which could be attributed to a normal response to a pathogen It is noteworthy that the occurrence of hyperferritinemia may be correlated with the development of the cytokine storm syndrome in the context of an inflammatory disease. In addition to adult onset Still's disease, macrophage activation syndrome, catastrophic anti-phospholipids syndrome, and septic shock, recent evidence has suggested this association between ferritin and life-threatening evolution in patients with systemic lupus erythematosus, with anti-MDA5 antibodies in the context of poly-dermatomyositis, with severe COVID-19, and with multisystem inflammatory syndrome. The possible underlying common inflammatory mechanisms, associated with hyperferritinemia, may led to the similar clinical picture observed in these patients. Furthermore, similar therapeutic strategies could be suggested inhibiting pro-inflammatory cytokines and improving long-term outcomes in these disorders. Thus, it could be possible to expand the spectrum of the hyperferritinemic syndrome to those diseases burdened by a dreadful clinical picture correlated with hyperferritinemia and the occurrence of the cytokine storm syndrome. In addition, the assessment of ferritin may provide useful information to the physicians in clinical practice to manage these patients. Therefore, ferritin may be considered a relevant clinical feature to be used as biomarker in dissecting the unmet needs in the management of these disorders. Novel evidence may thus support an expansion of the spectrum of the hyperferritinemic syndrome to these diseases burdened by a life-threatening clinical picture correlated with hyperferritinemia and the occurrence of the cytokine storm syndrome.

Iron Deficiency and Anemia in Cancer Patients: The Role of Iron Treatment in Anemic Cancer Patients

Anemia is a prevalent complication in patients with cancer, both at diagnosis and during treatment, with notable negative effects on quality of life and overall prognosis. Iron deficiency is the most common cause of anemia in the patients and can affect almost half of patients with solid and hematologic malignancies. The pathogenesis is complex and multifactorial, including bleeding, malnutrition, medications, and inflammation resulted from cancer and cancer treatment. In fact, either absolute or functional iron deficiency can occur. Most iron deficient cancer patients present with functional iron deficiency, a condition with adequate iron storage but insufficient iron supply for erythroblasts and other iron dependent tissues. Functional iron deficiency is the result of the cancer related cytokine release, but in absolute iron deficiency iron reserves are depleted leading to similar but often more severe symptoms of inadequate iron store. Current therapeutic options in cancer anemia consist of iron administration, erythropoietic stimulating agents, and blood transfusion. The latter should be administered to a minimum, because of problems regarding risks. Here, we present a review on the epidemiology, pathophysiology, clinical outcomes, and therapeutic options of iron deficiency as well as the effect of iron therapy on tumor progression in anemic cancer patients.

Epidemiological and nonclinical studies investigating effects of iron in carcinogenesis--a critical review

The efficacy and tolerability of intravenous (i.v.) iron in managing cancer-related anemia and iron deficiency has been clinically evaluated and reviewed recently. However, long-term data in cancer patients are not available; yet, long-term i.v. iron treatment in hemodialysis patients is not associated with increased cancer risk. This review summarizes epidemiological and nonclinical data on the role of iron in carcinogenesis. In humans, epidemiological data suggest correlations between certain cancers and increased iron exposure or iron overload. Nonclinical models that investigated whether iron can enhance carcinogenesis provide only limited evidence relevant for cancer patients since they were typically based on high iron doses as well as injection routes and iron formulations which are not used in the clinical setting. Nevertheless, in the absence of long-term outcome data from prospectively defined trials in i.v. iron-treated cancer patients, iron supplementation should be limited to periods of concomitant anti-tumor treatment.

Prevalence and management of cancer-related anaemia, iron deficiency and the specific role of i.v. iron

BACKGROUND

Chronic diseases reduce the availability of iron for effective erythropoiesis. This review summarises clinical consequences of iron deficiency (ID) and anaemia in cancer patients, mechanisms how impaired iron homeostasis affects diagnosis and treatment of ID, and data from clinical trials evaluating i.v. iron with or without concomitant erythropoiesis-stimulating agents (ESAs).

DESIGN

Clinical trial reports were identified in PubMed and abstracts at relevant major congresses.

RESULTS

Reported prevalence of ID in cancer patients ranges from 32 to 60% and most iron-deficient patients are also anaemic. Randomised clinical trials have shown superior efficacy of i.v. iron over oral or no iron in reducing blood transfusions, increasing haemoglobin, and improving quality of life in ESA-treated anaemic cancer patients. Furthermore, i.v. iron without additional ESA should be evaluated as potential treatment in patients with chemotherapy-induced anaemia. At recommended doses, i.v. iron is well tolerated, particularly compared with oral iron. No serious drug-related adverse effects were seen during long-term use in renal disease and no effect on tumour growth has been observed in trials with anaemic cancer patients.

CONCLUSIONS

Reliable diagnosis and treatment of ID are recommended key steps in modern cancer patient management to minimise impact on quality of life and performance status.

HFE, MTHFR, and FGFR4 genes polymorphisms and breast cancer in Brazilian women

Genetic factors related to cancer have been extensively studied and several polymorphisms have been associated to breast cancer. The FGFR4, MTHFR, and HFE genes have been associated with neoplastic diseases development. The current report outlines the analysis of the polymorphisms G388A (FGFR4), C677T (MTHFR), C282Y, and H63D (HFE) in Brazilian breast cancer patients. We studied 68 patients with invasive ductal and operable breast carcinoma and 85 women as a control group. The polymorphism frequencies in the breast cancer and control groups were analyzed, but no significant difference was observed by comparing the two groups. The presence of each polymorphism was analyzed according to the clinical features and markers already established as prognostic in the breast cancer group. The C677T, H63D, and G388A polymorphisms were not associated to histological grade, age of diagnosis, expression of HER2 receptor, or estrogen and progesterone receptor. The H63D polymorphism showed a significant association (P = 0.02) with the presence of p53 mutations, and C667T showed association to lymph node involvement (P = 0.05). Lymph node involvement, G388A polymorphism, and histological grade were independently associated to metastasis/death. Our data suggests that the polymorphisms G388A, C677T, and H63D are not useful in breast cancer diagnosis, but they may be significant additional prognostic markers related to breast cancer survival.

Dietary and stored iron as predictors of breast cancer risk: A nested case-control study in Shanghai

Increases in risk of breast cancer in successive generations of migrants to the United States from China and rapid temporal changes in incidence rates in China following social and economic changes clearly implicate environmental factors in the etiology of this disease. Case-control and cohort studies have provided evidence that at least some of these factors may be dietary. Iron, an essential element necessary for cell function, has also been demonstrated to have potential carcinogenic and co-carcinogenic activities. Iron overload, which was previously uncommon, has become more common in the United States than iron deficiency and may be increasing in China concurrently with dramatic increases in meat consumption. A case-control study nested in a cohort of women in Shanghai, China, was conducted to evaluate possible associations between risk of proliferative and nonproliferative fibrocystic changes as well as breast cancer and dietary iron intake and plasma ferritin levels. Plasma ferritin levels and reported dietary iron intake were compared in 346 women with fibrocystic changes, 248 breast cancer cases and 1,040 controls. Increasing ferritin levels were significantly associated with increasing risk of nonproliferative fibrocystic changes (OR: 2.51, 95% CI: 1.16-5.45, p trend = 0.04). Similar, but weaker, trends were observed for proliferative changes and for breast cancer. Risk of breast cancer relative to the risk of fibrocystic changes was associated with dietary iron intake in women with nonproliferative fibrocystic changes (OR: 2.63, 95% CI: 1.04-6.68, p = 0.02). In conclusion, this study finds significant associations between iron (stored and dietary) and fibrocystic disease and breast cancer.

HFE H63D mutation frequency shows an increase in Turkish women with breast cancer

BACKGROUND

The hereditary hemochromatosis gene HFE plays a pivotal role in iron homeostasis. The association between cancer and HFE hetero- or homozygosity has previously been shown including hepatocellular and nonhepatocellular malignancies. This study was performed to compare frequencies of HFE C282Y and H63D variants in Turkish women with breast cancer and healthy controls.

METHODS

Archived DNA samples of Hacettepe University Oncology Institute were used in this study. The HFE gene was investigated by PCR-RFLP.

RESULTS

All subjects studied were free from C282Y mutation. Thirty-nine patients had H63D mutation and were all heterozygous. H63D allele frequency was 22.2% (39/176) in the breast cancer patients, and 14% (28/200) in the healthy volunteers. Statistical analysis of cases with HFE H63D phenotype showed significant difference between breast cancer and healthy volunteers (P = 0.02).

CONCLUSION

Our results suggest that HFE H63D mutation frequencies were increased in the breast cancer patients in comparison to those in the general population. Also, odds ratios (odds ratio = 2.05) computed in this study suggest that H63D has a positive association with breast cancer.

Increased Prevalence of the HFE C282Y Hemochromatosis Allele in Women with Breast Cancer

Individuals with the major hemochromatosis (HFE) allele C282Y and iron overload develop hepatocellular and some extrahepatic malignancies at increased rates. No association has been previously reported between the C282Y allele and breast cancer. We hypothesized that due to the pro-oxidant properties of iron, altered iron metabolism in C282Y carriers may promote breast carcinogenesis. Because 1 in 10 Caucasians of Northern European ancestry carries this allele, any impact it may have on breast cancer burden is potentially great. We determined C282Y genotypes in 168 patients who underwent high-dose chemotherapy and blood cell transplantation for cancer: 41 with breast cancer and 127 with predominantly hematological cancers (transplant cohort). Demographic, clinical, and tumor characteristics were reviewed in breast cancer patients. The frequency of C282Y genotypes in breast cancers was compared with the frequency in nonbreast cancers, an outpatient sample from Tennessee (n = 169), and a published United States national sample. The frequency of at least one C282Y allele in breast cancers was higher (36.6%, 5 homozygotes/10 heterozygotes) than frequencies in Tennessee (12.7%, P < 0.001), the general population (12.4%, P < 0.001), and similarly selected nonbreast cancers (17.0%, P = 0.008). The likelihood of breast cancer in the transplant cohort increased with C282Y allele dose (P(trend) = 0.010). These results were supported by the finding in a nontransplant cohort of a higher frequency of C282Y mutations in Caucasian (18.4%, P = 0.039) and African-American (8.5%, P = 0.005) women with breast cancer than race-specific national frequency estimates. A high prevalence of C282Y alleles in women with breast cancer with and without poor risk features suggests that altered iron metabolism in C282Y carriers may promote the development of breast cancer and/or more aggressive forms of the disease.

Chemoprevention of DMBA-induced mammary gland carcinogenesis--preventive effects of free oxygen radical scavengers

This study was carried out to determine the effects of Mangan-Desferrioxamine (Mn-DFX) and Verapamil (VRP) in 7,12-dimethyl-benz-[a]anthracene (DMBA) induced mammary carcinoma. 70 Spraque Dawley rats were divided into four groups; as DMBA alone, DMBA + Mn-DFX, DMBA + VRP, and control. Incidence, multiplicity, and size of tumors were evaluated in addition to analyses of DNA ploidy status and proliferation index by flow cytometric technique. The results revealed that Mn-DFX and VRP caused significant decreases in tumor incidence (p < 0.02 and p < 0.05), multiplicity (p < 0.02 and p < 0.05), size (p < 0.05 and p < 0.02), and proliferation index (p < 0.05 and p < 0.02) without any toxic effect. The appearance of first tumors in Mn-DFX and VRP groups was also later than in the DMBA alone group (10th and 11th week versus 6th week). In conclusion, Mn-DFX and VRP have offered prevention in experimental mammary carcinogenesis. These agents caused slower tumor growth, though they could not achieve a complete prevention.

The molecular mechanisms of the metabolism and transport of iron in normal and neoplastic cells

Iron uptake by mammalian cells is mediated by the binding of serum Tf to the TfR. Transferrin is then internalized within an endocytotic vesicle by receptor-mediated endocytosis and the Fe released from the protein by a decrease in endosomal pH. Apart from this process, several cell types also have other efficient mechanisms of Fe uptake from Tf that includes a process consistent with non-specific adsorptive pinocytosis and a mechanism that is stimulated by small-Mr Fe complexes. This latter mechanism appears to be initiated by hydroxyl radicals generated by the Fe complexes, and may play a role in Fe overload disease where a significant amount of serum non-Tf-bound Fe exists. Apart from Tf-bound Fe uptake, mammalian cells also possess a number of mechanisms that can transport Fe from small-Mr Fe complexes into the cell. In fact, recent studies have demonstrated that the membrane-bound Tf homologue, MTf, can bind and internalize Fe from 59Fe-citrate. However, the significance of this Fe uptake process and its pathophysiological relevance remain uncertain. Iron derived from Tf or small-Mr complexes is probably transported into mammalian cells in the Fe(II) state. Once Fe passes through the membrane, it then becomes part of the poorly characterized intracellular labile Fe pool. Iron in the labile Fe pool that is not used for immediate requirements is stored within the Fe-storage protein, ferritin. Cellular Fe uptake and storage are coordinately regulated through a feedback control mechanism mediated at the post-transcriptional level by cytoplasmic factors known as IRP1 and IRP2. These proteins bind to stem-loop structures known as IREs on the 3 UTR of the TfR mRNA and 5 UTR of ferritin and erythroid delta-aminolevulinic acid synthase mRNAs. Interestingly, recent work has suggested that the short-lived messenger molecule, NO (or its by-product, peroxynitrite), can affect cellular Fe metabolism via its interaction with IRP1. Moreover, NO can decrease Fe uptake from Tf by a mechanism separate to its effects on IRP1, and NO may also be responsible for activated macrophage-mediated Fe release from target cells. On the other hand, the expression of inducible NOS which produces NO, can be stimulated by Fe chelators and decreased by the addition of Fe salts, suggesting that Fe is involved in the control of NOS expression.

A phase II trial of deferoxamine in patients with hormone-refractory metastatic prostate cancer

The management of hormone-refractory metastatic prostate cancer remains a therapeutic dilemma. We report the results of a phase II trial with deferoxamine administrated at a dose of 50 mg/kg (maximum dose 5 g) administered intravenously over 8 hr daily, repeated for 5 days at 4-week intervals for 2 courses. Fourteen patients with advanced hormone-refractory prostate cancer were treated and 28 courses were delivered. Essentially no toxicity was observed. Using combined clinical and prostate-specific antigen (PSA) criteria. 13 of 14 patients had disease progression. However, 9 of 14 patients had stable measurable or evaluable disease and progressed solely based on PSA criteria. Deferoxamine in this dose and schedule has no activity in hormone-refractory prostate cancer. Further investigation of the effect of deferoxamine on PSA production/expression is warranted.

Use of Mishell-Dutton culture for the detection of the immunosuppressive effect of iron-containing compounds

Mishell-Dutton culture, known as an in vitro model for the evaluation of the humoral immune response of mice spleen cells to sheep red blood cells (SRBC), was used to study the immunosuppressive effect of iron-containing compounds. This response was indicated by the number of antibody forming cell (AFC) per million nucleated cells. Ferrous sulfate and ferric citrate (0.1 mM), when continuously present in Mishell-Dutton culture, significantly decreased the SRBC AFC response by approximately 63% and 86% of the control values, respectively. Ferric citrate, preincubated (24 h) with spleen cells and followed by lavage, significantly decreased the SRBC AFC response by approximately 54% of the control values. Primary and iron-treated coal, in concentrations ranging from 40 micrograms.ml-1 to 120 micrograms.ml-1, significantly decreased the SRBC AFC response when continuously present in Mishell-Dutton culture. Iron-treated coal, suppressed this response, in dose-dependent amounts, to a greater extent than did the primary coal:73% versus 54% at 120 micrograms.ml-1. We concluded that Mishell-Dutton culture is suitable for studying the immunotoxicity of iron and these results may contribute to explain a decrease of host resistance against parasitic and bacterial infection in workers exposed to iron.

Increased liver iron stores in patients with hepatocellular carcinoma developed on a noncirrhotic liver

Iron was systematically studied in the nontumorous liver of 24 patients with hepatocellular carcinoma (HCC) developed on a noncirrhotic liver compared with 4 control groups (cirrhosis with and without HCC, liver metastasis, and normal liver) matched according to age, sex, and presence of chronic alcoholism. Assessment of liver iron was made by (1) histology according to iron distribution and quantification (total iron score: 0 to 60), and (2) biochemistry (liver iron concentration-N < 36 mumol/g) with calculation of the hepatic iron index (liver iron concentration/age). Patients with hepatocellular carcinoma developed on a noncirrhotic liver presented with (1) histological iron in 83%; (2) parenchymal iron excess significantly more frequent (90%) than in controls; (3) total iron score (15 +/- 12) and liver iron concentration (81 +/- 96) significantly greater than in controls; and (4) hepatic iron index significantly increased (1.4 +/- 1.5) when compared with control groups, except for the hepatocellular carcinoma complicating cirrhosis group (0.9 +/- 1.1). This study (1) shows a mild but unquestionable parenchymal iron excess in the nontumorous liver of most patients presenting with hepatocellular carcinoma developed on a noncirrhotic liver and, at a lesser extent, on cirrhosis, (2) should incite others to study the putative role of iron in the development of liver cancer both in patients with cirrhosis and those without it, whatever the cause of the underlying liver disease, and (3) add argument to take into account and to treat any liver iron excess, even when mild.

Diet, serum markers and breast cancer mortality in China

This county-based correlation study examined associations of breast cancer mortality with dietary habits and certain serum biochemical markers, utilizing data collected from an ecological survey in 65 Chinese rural counties. Univariate correlation and multivariate regression analysis showed that consumption of animal foods, including eggs, fish and meat, was positively linked to county-wide mortality rates of breast cancer in Chinese women. No clear associations between breast cancer mortality rates and consumption of green vegetables, carrots and fruits were observed in this study. A modest inverse correlation between serum vitamin C levels and breast cancer mortality was observed, while selenium levels were positively related to the mortality rates. Positive correlations for serum ferritin and hemoglobin were found, in agreement with recent reports of an elevated cancer risk with increased body iron stores. Limitations of these ecological data preclude causal inferences, but the findings provide clues to breast cancer risk and protective factors in a low incidence area of the world.

Most free-radical injury is iron-related: it is promoted by iron, hemin, holoferritin and vitamin C, and inhibited by desferoxamine and apoferritin

Iron is a double-edged sword. In moderate quantities and leashed to protein, it is an essential element in all cell metabolism and growth, but it is toxic when unleashed. Because of its ability to switch back and forth between ferrous and ferric oxidation states, iron is both a strong biological oxidant and reductant. The human diet contains a multitude of natural chemicals which are carcinogens and anticarcinogens, many of which act by generating oxygen radicals, which initiate degenerative processes related to cancer, heart disease and aging (the "oxygen radical hypothesis of aging"). Among these many dietary chemicals are many redox agents, including vitamin C and beta carotene. Free radical damage is produced primarily by the hydroxyl radical (.OH). Most of the .OH generated in vivo comes from iron-dependent reduction of H2O2. Supporting too much iron as a free radical-generating culprit in the risk of cancer, NHANES I data indicated that high body iron stores, manifested by increased transferrin saturation, are associated with an increased cancer risk. Other data shows an increased heart attack risk.

Moderate elevation of body iron level and increased risk of cancer occurrence and death

The purpose of the study was to address the hypothesis that elevated body iron increases the risk of cancer occurrence and death, and to determine the dose response. Subjects were 3,287 men and 5,269 women participating in the first National Health and Nutrition Examination Survey who had a transferrin saturation determination at enrollment (1971-1975), who remained alive and cancer-free for at least 4 years, and who were followed to 1988 for cancer outcome. Among 379 men who developed cancer over the study period, the mean transferrin saturation at enrollment was 32.1% whereas among 2,908 who remained cancer-free it was 30.7%; the difference for mortality was 32.3% among 233 deaths vs. 30.8% among 3,054 men not dying of cancer. The mean differences among women were not significant. The mean differences in TIBC and serum iron among men were consistent with the findings for transferrin saturation, and all 3 differences were stable over time when examined by years since blood test. Men and women were divided into 5 groups on the basis of baseline transferrin saturation: 0 to 30%, 30-40%, 40-50%, 50-60%, and 60% and higher. Nineteen percent of men had a baseline transferrin saturation above 40% (the last 3 groups), whereas only 10 percent of women had transferrin saturation above 40%. For men and women combined, risk of cancer occurrence in each group relative to the first was 1.0, 0.95, 1.16, 1.38 and 1.81; for mortality the relative risks were 1.0, 0.96, 1.22, 1.29 and 1.73. There is evidence, in this cohort, of elevated cancer risk in those with moderately elevated iron level. This pattern was seen in women as well as in men.

Roles of iron in neoplasia. Promotion, prevention, and therapy

Research and clinical observations during the past six decades have shown that: 1. Iron promotes cancer cell growth; 2. Hosts attempt to withhold or withdraw iron from cancer cells; and 3. Iron is a factor in prevention and in therapy of neoplastic disease. Although normal and neoplastic cells have similar qualitative requirements for iron, the neoplastic cells have more flexibility in acquisition of the metal. Excessive iron levels in animals and humans are associated with enhanced neoplastic cell growth. In invaded hosts, cytokine-activated macrophages increase intracellular ferritin retention of the metal, scavenge iron in areas of tumor growth, and secrete reactive nitrogen intermediates to effect efflux of nonheme iron from tumor cells. Procedures associated with lowering host intake of excess iron can assist in prevention and in management of neoplastic disease. Chemical methods for prevention of iron assimilation by neoplastic cells are being developed in experimental and clinical protocols. The antineoplastic activity of a considerable variety of chemicals, as well as of radiation, is modulated by iron. The present article focuses on recent findings and suggests directions for further cancer-iron research.

Iron, radiation, and cancer

Increased iron content of cells and tissue may increase the risk of cancer. In particular, high available iron status may increase the risk of a radiation-induced cancer. There are two possible mechanisms for this effect: iron can catalyze the production of oxygen radicals, and it may be a limiting nutrient to the growth and development of a transformed cell in vivo. Given the high available iron content of the western diet and the fact that the world is changing to the western model, it is important to determine if high iron increases the risk of cancer.

The uptake of iron and transferrin by the human malignant melanoma cell

The role of the transferrin homologue, melanotransferrin (p97), in iron metabolism has been studied using the human melanoma cell line, SK-MEL-28, which expresses this antigen in high concentrations. The mechanisms of iron and transferrin uptake were investigated using human transferrin labelled with iodine-125 and iron-59. Internalised and membrane-bound iron and transferrin were separated using the proteinase, pronase. The uptake of iron from transferrin occurred by at least two processes. The first process was saturable and consistent with receptor-mediated endocytosis, involving internalisation of transferrin bound to specific binding sites. Uptake of iron also occurred by a second process which was non-saturable up to 0.06 mg/ml (0.75 microM) and was of higher efficiency than the saturable process. This process of iron uptake may be the dominant one at physiological serum transferrin concentrations. A membrane-bound, pronase-sensitive, temperature-dependent, iron-binding component was also identified. The number of binding sites was estimated to be approx. 340,000 per cell (assuming 2 atoms of iron per site) and it is suggested that this binding component may be melanotransferrin.

Body iron stores and the risk of cancer

Because of evidence that increased body iron stores are associated with an increased risk of cancer, we examined iron status and cancer risk in the first National Health and Nutrition Examination Survey, a survey of more than 14,000 adults begun in 1971, with follow-up between 1981 and 1984. Among 242 men in whom cancer developed, the mean total iron-binding capacity was significantly lower (61.4 vs. 62.9 mumol per liter; P = 0.01) and transferrin saturation was significantly higher (33.1 vs. 30.7 percent; P = 0.002) than among 3113 men who remained free of cancer. The risk of cancer in men in each quartile of transferrin-saturation level relative to the lowest quartile was 1.00, 1.01, 1.10, and 1.37 (P = 0.02 for trend). The serum albumin level was significantly lower in men in whom cancer developed than in those who remained cancer-free. Among women, those in whom cancer developed did not have significantly lower total iron-binding capacity or higher transferrin saturation than those who remained cancer-free. However, a post hoc examination of 5367 women (203 with cancer) yielded a relative risk of 1.3 (95 percent confidence interval, 0.9 to 1.9) associated with a very high transferrin saturation (greater than or equal to 36.8 percent, a value in the highest quartile among men); in 5228 women with at least six years of follow-up (149 with cancer), the relative risk associated with transferrin saturation above this level was 1.5 (1.0 to 2.2). These results are consistent with the hypothesis that high body iron stores increase the risk of cancer in men. The possibility that a similar association exists in women requires further study.

Iron status and cellular immune competence

There is increasing evidence that both iron overload and iron deficiency are associated with significant abnormalities of immune function. In diseases associated with iron overload there is increased susceptibility to both infection and neoplasia. The precise mechanisms are still being unravelled but iron overload has been shown to impair antigen-specific immune responses and to reduce the number of functional helper precursor cells. Similarly, iron in vitro in concentrations reported to be present in the serum of patients with iron overload impairs the generation of cytotoxic T-cells, enhances suppressor T-cell activity and reduces the proliferative capacity of helper T-cells. The predominant tumor seen in iron overload is primary hepatocellular carcinoma; however other aetiological factors appear to be involved in addition to iron overload, especially hepatic cirrhosis. Nevertheless, primary liver cancer occurs much more frequently in hemochromatosis than in other forms of cirrhosis. Iron deficiency is associated with an altered response to infection but the relationship is again a complex one. The cellular mechanisms involved have yet to be clearly defined, although impaired T and B cell function have been demonstrated.