Toenail-Based Metal Concentrations and Young-Onset Breast Cancer

Lead (Pb) in biological samples in association with cancer risk and mortality: A systematic literature review

BACKGROUND AND AIM

Lead (Pb) is a toxic heavy metal and pervasive environmental contaminant, and a class 2 A carcinogen according to the IARC classification, yet its link with cancer at several body sites remains uncertain. Here, we aimed at summarizing the scientific evidence regarding its association with cancer risk and mortality, focusing on studies that carried out Pb measurements in biological samples.

METHODS

We reviewed articles published in PubMed and EMBASE until January 2nd, 2024, that quantified the epidemiological association between Pb measured in blood, urine, nails, and other biological media, and cancer risk and mortality (overall and by cancer site/type).

RESULTS

We included 46 articles (out of 8022 screened) published in 1995-2023 and reporting on investigations conducted in fifteen countries. In terms of design, 20 were prospective, 24 were retrospective case-control studies, and 2 were cross-sectional. Pb levels were determined in blood in the majority of studies (n=28). The most consistent evidence was for the association of Pb with cancer of the gastrointestinal tract, particularly the oesophagus, stomach (RR ranging from 0.80 to 2.66), colon-rectum, and pancreas; and of the bladder and urinary tract (RR from 1.10 to 2.89). For other specific malignancies, the data were conflicting or too limited to draw reliable conclusions. Finally, increased Pb concentration in blood and urine was consistently associated with higher overall cancer incidence and mortality.

CONCLUSIONS

Lead is a widespread and highly persistent environmental pollutant associated with cancer at multiple body sites. Comprehensive primary prevention interventions aiming at reducing opportunities for Pb exposure need to be continuously promoted and implemented.

Heavy-metal associated breast cancer and colorectal cancer hot spots and their demographic and socioeconomic characteristics

PURPOSE

Cancer registries offer an avenue to identify cancer clusters across large populations and efficiently examine potential environmental harms affecting cancer. The role of known metal carcinogens (i.e., cadmium, arsenic, nickel, chromium(VI)) in breast and colorectal carcinogenesis is largely unknown. Historically marginalized communities are disproportionately exposed to metals, which could explain cancer disparities. We examined area-based metal exposures and odds of residing in breast and colorectal cancer hotspots utilizing state tumor registry data and described the characteristics of those living in heavy metal-associated cancer hotspots.

METHODS

Breast and colorectal cancer hotspots were mapped across Kentucky, and area-based ambient metal exposure to cadmium, arsenic, nickel, and chromium(VI) were extracted from the 2014 National Air Toxics Assessment for Kentucky census tracts. Among colorectal cancer (n = 56,598) and female breast cancer (n = 77,637) diagnoses in Kentucky, we used logistic regression models to estimate Odds Ratios (ORs) and 95% Confidence Intervals to examine the association between ambient metal concentrations and odds of residing in cancer hotspots, independent of individual-level and neighborhood risk factors.

RESULTS

Higher ambient metal exposures were associated with higher odds of residing in breast and colorectal cancer hotspots. Populations in breast and colorectal cancer hotspots were disproportionately Black and had markers of lower socioeconomic status. Furthermore, adjusting for age, race, tobacco and neighborhood factors did not significantly change cancer hotspot ORs for ambient metal exposures analyzed.

CONCLUSION

Ambient metal exposures contribute to higher cancer rates in certain geographic areas that are largely composed of marginalized populations. Individual-level assessments of metal exposures and cancer disparities are needed.

Seasonal patterns in trace elements assessed in toenails

BACKGROUND

Seasonal patterns in measured exposure biomarkers can cause measurement error in epidemiological studies. There is little research about the seasonality of metals and trace elements when assessed in toenail samples. Adjusting for such patterns in models for estimating associations between long-term exposures and health outcomes can potentially improve precision and reduce bias.

OBJECTIVES

Assess and describe seasonal patterns in toenail measurements of trace elements.

METHODS

The Sister Study enrolled women residing in the US, including Puerto Rico, whose sister had been diagnosed with breast cancer. At the time of enrollment, participants removed nail polish and collected their toenail clippings, which were cleaned before analysis. We considered the following elements: iron, vanadium, aluminum, chromium, manganese, cobalt, nickel, copper, zinc, arsenic, selenium, molybdenum, cadmium, tin, antimony, mercury, and lead. For two subsamples of the cohort, we fit trigonometric regression models with toenail element measures as the outcome, using sine and cosine functions of the collection day (transformed to an angle) to capture seasonal patterns. These models can estimate the amplitude and timing of the peaks in measures. We evaluated the evidence for a seasonal effect by comparing for each measured element the trigonometric model to a model that was constant across time.

RESULTS

There was a seasonal trend in toenail element concentration for iron, aluminum, vanadium, chromium, manganese, cobalt, arsenic, molybdenum, cadmium, tin, and lead, all of which peaked near mid-August. Seasonal patterns were concordant across two non-overlapping samples of women, analyzed in different labs.

DISCUSSION

Given the evidence supporting seasonal patterns for 11 of the 17 elements measured in toenails, correcting for seasonality of toenail levels of those trace elements in models estimating the association between those exposures and health outcomes is important. The basis for higher concentrations in toenails collected during the summer remains unknown.

Update of the risk assessment of inorganic arsenic in food

The European Commission asked EFSA to update its 2009 risk assessment on arsenic in food carrying out a hazard assessment of inorganic arsenic (iAs) and using the revised exposure assessment issued by EFSA in 2021. Epidemiological studies show that the chronic intake of iAs via diet and/or drinking water is associated with increased risk of several adverse outcomes including cancers of the skin, bladder and lung. The CONTAM Panel used the benchmark dose lower confidence limit based on a benchmark response (BMR) of 5% (relative increase of the background incidence after adjustment for confounders, BMDL05) of 0.06 μg iAs/kg bw per day obtained from a study on skin cancer as a Reference Point (RP). Inorganic As is a genotoxic carcinogen with additional epigenetic effects and the CONTAM Panel applied a margin of exposure (MOE) approach for the risk characterisation. In adults, the MOEs are low (range between 2 and 0.4 for mean consumers and between 0.9 and 0.2 at the 95th percentile exposure, respectively) and as such raise a health concern despite the uncertainties.

Potential Health Effects of Heavy Metals and Carcinogenic Health Risk Estimation of Pb and Cd Contaminated Eggs from a Closed Gold Mine Area in Northern Thailand

Gold-mining activities have been demonstrated to result in significant environmental pollution by Hg, Pb, and Mn, causing serious concerns regarding the potential threat to the public health of neighboring populations around the world. The present study focused on heavy-metal contamination in the eggs, blood, feed, soil, and drinking water on chicken farms, duck farms, and free-grazing duck farms located in areas < 25 km and > 25 km away from a gold mine in northern Thailand. In an area < 25 km away, Hg, Pb, and Mn concentrations in the eggs of free-grazing ducks were significantly higher than > 25 km away (p < 0.05). In blood, Hg concentration in free-grazing ducks was also significantly higher than those in an area > 25 km away (p < 0.05). Furthermore, the Pb concentration in the blood of farm ducks was significantly higher than in an area > 25 km away (p < 0.05). The concentration of Cd in drinking water on chicken farms was significantly higher for farms located within 25 km of the gold mine (p < 0.05). Furthermore, a high correlation was shown between the Pb (r2 = 0.84) and Cd (r2 = 0.42) found between drinking water and blood in free-grazing ducks in the area < 25 km away. Therefore, health risk from heavy-metal contamination was inevitably avoided in free-grazing activity near the gold mine. The incremental lifetime cancer risk (ILCR) in the population of both Pb and Cd exceeded the cancer limit (10−4) for all age groups in both areas, which was particularly high in the area < 25 km for chicken-egg consumption, especially among people aged 13−18 and 18−35 years old. Based on these findings, long-term surveillance regarding human and animal health risk must be strictly operated through food chains and an appropriate control plan for poultry businesses roaming around the gold mine.

Metals and Breast Cancer Risk: A Prospective Study Using Toenail Biomarkers

The role of metals in breast cancer is of interest because of their carcinogenic and endocrine-disrupting capabilities. Evidence from epidemiologic studies remains elusive, and prior studies have not investigated metal mixtures. In a case cohort nested within the Sister Study (enrolled in 2003-2009; followed through September 2017), we measured concentrations of 15 metals in toenails collected at enrollment in a race/ethnicity-stratified sample of 1,495 cases and a subcohort of 1,605 women. We estimated hazard ratios and 95% confidence intervals for each metal using Cox regression and robust variance. We used quantile g-computation to estimate the joint association between multiple metals and breast cancer risk. The average duration of follow-up was 7.5 years. There was little evidence supporting an association between individual metals and breast cancer. An exception was molybdenum, which was associated with reduced incidence of overall breast cancer risk (third tertile vs. first tertile: hazard ratio = 0.82, 95% confidence interval: 0.67, 1.00). An inverse association for antimony was observed among non-Hispanic Black women. Predefined groups of metals (all metals, nonessential metals, essential metals, and metalloestrogens) were not strongly associated with breast cancer. This study offers little support for metals, individually or as mixtures, as risk factors for breast cancer. Mechanisms for inverse associations with some metals warrant further study.