Lead Exposure: A Contributing Cause of the Current Breast Cancer Epidemic in Nigerian Women

Breast cancer incidence in Nigerian women has significantly increased during the
past three decades in parallel with the rapid industrialization of that country. This suggested
that the associated widespread contamination of the soil and of the water supplies by lead
(Pb) and other industrial metals was a major contributing cause. Because of its many
domestic, industrial, and automotive uses, Pb is of particular concern as it has been shown
to promote the development of mammary tumors in murine mammary tumor virus-infected
female C3H mice at levels as low of 0.5 ppm Pb in the drinking water. Lead belongs to the
group of selenium-antagonistic elements that interact with selenium (Se), abolishing its
anti-carcinogenic effect. Lead on chronic, low-level exposure in addition also accelerates
tumor growth rates. Higher levels of Pb were found in blood and head hair samples of
newly diagnosed patients with breast cancer, all with infiltrating ductal carcinoma, the most
common form of breast cancer in Nigeria, seen at Obafemi Awolowo University, than in
cancer-free controls from the same area. Evidence for interactions between Pb and Se was
obtained from blood, hair, and tumor biopsy tissue analyses. Furthermore, the Pb levels in
hair samples of the patients were directly correlated with the volumes of their tumors, in
accord with the tumor growth-promoting effects of Pb. Conversely, Se levels in hair and
blood were inversely correlated with the tumor volumes, consistent with the antiproliferative
effects of Se. Several other elements, e.g., Cd, Hg, Cr, Sn, and As, were
detected in the scalp hair of the patients and the controls, although at significantly lower
levels than those of Pb. However, correlation calculations revealed them also to interact
with Se, suggesting that only a fraction of the Se in organs and tissues is actually present in
bioactive forms. In metal-exposed subjects, a state of latent Se deficiency may exist,
resulting in depressed immune functions and increased cancer susceptibility. Evidence is
presented to show that Pb and other metals also interact with iodine, another vitally
important essential trace element believed to protect against breast cancer development.
Public health programs aiming at lowering the breast cancer risk of Nigerian women thus
will have to include effective measures to protect the population from exposures to Pb and
other industrial metals that are presently contaminating the environment and the water