Lead (Pb) exposure from outdoor air pollution: a potential risk factor for cervical intraepithelial neoplasia related to HPV genotypes

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.

The Relationship Between Metal Exposure and HPV Infection: Evidence from Explainable Machine Learning Methods

HPV is a ubiquitous pathogen implicated in cervical and other cancers. Although vaccines are available, they do not encompass all subtypes. Meanwhile, metal exposure may elevate the risk of HPV infection and amplify its carcinogenic potential, but studies to further elucidate this relationship are insufficient. This study entailed a cross-sectional analysis utilizing data from the National Health and Nutrition Examination Survey (NHANES) 2007-2016. The study sample comprised 2765 women. Multivariate logistic regression was employed to examine the association between single metal exposure and HPV infection, weighted quantile sum (WQS) regression was utilized for assessing the mixed metal exposure effect, and the XGBoost + SHapley Additive exPlanations (SHAP) to evaluate the contribution of metal exposure in HPV infection. Multivariate logistic regression analysis indicated that elevated Co concentration was inversely associated with HPV infection (OR 0.891; 95% CI 0.814-0.975), while elevated Pb concentration correlated with an increased HPV infection (OR 1.176; 95% CI 1.074-1.287). Regression analysis of the WQS for mixed metal exposure suggested that the WQS index was potentially linked to an increased likelihood of HPV infection in the positive direction (OR 1.249; 95% CI 1.052-1.482), with no significant association observed in the negative direction (OR 0.852; 95% CI 0.713-1.017). SHAP analysis prioritized the importance of characteristics: number of sexual partners, marital status, poverty-to-income ratio (PIR), Co, Pb, and alcohol consumption. Exposure to Pb was associated with an increase in the incidence of HPV infection, whereas Co exposure demonstrated an inverse relationship. The composite exposure to multiple metals showed a positive association with the prevalence of HPV infection. These findings indicate that exposure to metals could potentially escalate the prevalence of HPV infection.

The Role of Lead and Cadmium in Gynecological Malignancies

Lead and cadmium are non-essential and toxic heavy metals. Their presence and elevated levels can lead to many pathologies. They disrupt the antioxidant properties of many enzymes, consume the resources of antioxidant cells, and thus participate in the generation of oxidative stress, which may result in DNA damage. In addition, they have been found to be carcinogenic through their genotoxic properties. They have been shown to be present in various types of cancer, including cancer of the female reproductive system. Both metals have been recognized as metalloestrogens, which are important in hormone-related cancers. Participation in the oncogenesis of ovarian, endometrial and cervical cancer was analysed in detail, using the available research in this field. We emphasize their role as potential biomarkers in cancer risk and diagnosis as well as advancement of gynaecological malignancies.