Air pollution has long been known to have detrimental effects on human health, but a recent study published in the Journal of the National Cancer Institute has brought attention to its potential link with breast cancer. Using a spatiotemporal model, researchers analyzed a large sample of women across the United States to investigate the relationship between air pollution and breast cancer risk.
The study found that for every 10 mg/m3 increase in estimated historic PM2.5 concentrations over a 10–15-year period, there was an 8 percent increase in breast cancer risk. PM2.5 refers to fine inhalable particles that pose the greatest health risk, according to the US Environmental Protection Agency.
While this study focused on the US population, it raises concerns about the impact of air pollution on breast cancer risk worldwide, especially in countries with high levels of pollution such as India. The Air Quality Life Index (AQLI) data reveals that residents in India, Bangladesh, Nepal, and Pakistan are expected to lose an average of 5 years of life expectancy due to pollution. Furthermore, a study by the University of Chicago found that 59 percent of the increase in world pollution since 2013 can be attributed to India alone.
In India, the situation is particularly alarming. All 1.4 billion people in the country live in areas where the annual average particulate pollution levels exceed the guidelines set by the World Health Organization (WHO). The WHO recommends a 24-hour average guideline of 5 micrograms per cubic meter (µg/m3) for PM2.5, while India’s national average concentration is 53.3 μg/m3.
Breast cancer is a significant concern in India, with gynecologic cancers accounting for 51 percent of all cancers among women, according to a report by the Indian Council for Medical Research. Given the already established association between PM and lung cancer, Indian oncologists are not surprised by the US study’s findings that PM may contribute to breast cancer risk.
Dr. Ruquaya Ahmad Mir, a Senior Consultant in Surgical Oncology, stated that low-dose long-term exposure to PM could result in increased incidence of other cancers such as lung and esophagus. However, Dr. Uma Dangi, a Consultant in Medical Oncology, points out that racial and ethnic differences between Caucasians and Asians, including Indians, may also contribute to different risk profiles for breast cancer.
Genetic factors play a significant role in breast cancer risk, and previous studies have shown that the frequency of BRCA1/2 genetic mutations is higher among Indian familial breast cancer patients compared to the general US population. BRCA1 and BRCA2 mutations can increase the chances of developing breast cancer, and their prevalence among Indian women could be a contributing factor.
While the US study focused on women over the age of 50, who are typically menopausal or post-menopausal, it is important to consider the impact of PM on breast cancer risk among pre-menopausal women as well. Dr. Dangi explains that breast cancer usually occurs in women over 50 in western countries, which could be why this age group was chosen for the study. The longer the exposure to environmental toxins, the higher the risk of developing cancer.
The study also found an association between particulate matter pollution and estrogen receptor-positive (ER+) breast tumors, which have receptors that bind to estrogen, promoting cell growth. These types of tumors respond well to hormonal treatments, such as Tamoxifen. However, there was no significant association found for estrogen receptor-negative (ER-) tumors, which do not respond well to hormonal treatments and tend to be more aggressive.
In India, there is a higher number of triple-negative breast cancer cases, where the cancer cells lack estrogen and progesterone receptors and do not produce the HER2 protein. This type of cancer tends to grow and spread faster, has fewer treatment options, and a worse prognosis. The incidence of estrogen-positive breast cancer, which is more common in the west, is lower in India.
It is important to note that more studies are needed to draw definitive conclusions about the association between air pollution and breast cancer risk in the Indian population. However, the findings of the US study and the high levels of pollution in India highlight the urgent need to address air pollution as a public health concern. Implementing measures to reduce pollution and raise awareness about its potential health risks, including breast cancer, could help protect the population from the harmful effects of air pollution.