Air Pollution May be Associated With Many Kinds of Cancer

Researchers urge better regulation to protect public health

It’s no surprise that air pollution has been linked with lung cancer.

A new study suggests that pollution is also associated with increased risk of mortality for several other types of cancer, including breast, liver, and pancreatic cancer.

A pair of researchers, one in Hong Kong and one in Birmingham, United Kingdom, studied long-term exposure to ambient fine particulate matter, a mixture of environmental pollutants that come from transportation and power generation, among other sources. Ambient fine particulate matter has an aerodynamic diameter of less than 2.5 micrometers and is known as PM_2.5.

The study enrolled 66,280 residents of Hong Kong, all of whom were age 65 or older when initially recruited between 1998 and 2001. The researchers followed the study subjects until 2011, ascertaining causes of death from Hong Kong registrations.

Annual concentrations of PM_2.5 at their homes were estimated using data from satellites and fixed-site monitors.

After adjusting for smoking status and excluding deaths that had occurred within three years of the baseline to control for competing diseases, the study showed that for every 10 microgram per cubic meter (µg/m3) of increased exposure to PM_2.5, risk of dying from any cancer rose by 22 percent.

For cancers of the upper digestive tract, the mortality risk was 42 percent higher.

For cancers of the accessory digestive organs, which include the liver, bile ducts, gall bladder, and pancreas, the mortality risk was 35 percent higher.

For breast cancer, the mortality risk was 80 percent higher.

And for lung cancer, the mortality risk was 36 percent higher. All figures are per 10 µg/m3 increased exposure to PM_2.5.

The authors identified a few potential explanations for the increased association: Pollution might spark defects in DNA repair function, alterations in the body’s immune response, or inflammation that triggers angiogenesis, the growth of new blood vessels that allows tumors to spread.

In the case of the digestive organs, pollution could affect gut microbiota and influence the development of cancer, they said.

G. Neil Thomas, MPhil, PhD, a reader in epidemiology in the Department of Public Health, Epidemiology and Biostatistics in the Institute of Applied Health of the College of Medical and Dental Sciences at The University of Birmingham, said further research would be required to determine whether other countries experience similar associations between PM_2.5 and cancer deaths, but this study combined with existing research suggests that other urban populations may carry the same risks.

“The implications for other similar cities around the world are that PM_2.5 must be reduced as much and as fast as possible,” he said. “Air pollution remains a clear, modifiable public health concern.”

The study’s other lead author, Thuan Quoc Thach, PhD, a scientific officer at the School of Public Health at the University of Hong Kong, noted that PM_2.5 is just one component of air pollution, and will require further study to confirm its effects.

Dr. Thach cautioned that pollution is just one risk factor for cancer, and others, such as diet and exercise, may be more significant and more modifiable risk factors.

This study follows a 2013 review by the International Agency for Research on Cancer (IARC) that determined that there is enough evidence to say that outdoor air pollution can cause cancer in people. That report also specifically implicated PM_2.5.