• A recent study analyzed worldwide trends of lung cancer, smoking rates, and air pollution.
• The authors found that rates of certain types of lung cancer are decreasing, while others are increasing.
• The recent rise in lung adenocarcinoma cases may correlate with a worldwide increase in air pollution.

A recent study concluded that reduced rates of smoking globally have contributed to the drop in lung squamous cell carcinoma (LSCC), while air pollution is contributing to increased rates of lung adenocarcinoma (LADC).

Lung Cancer and Air Pollution

Lung cancer is the leading cause of cancer deaths around the globe. Along with cigarette smoking, air pollution is a common cause of lung cancer. Particles from vehicle exhaust, industrial plants, and other sources may contain cancer-causing chemicals that can lead to diseases of the lungs, such as asthma. Small particles that are inhaled can become trapped deep in the lungs, eventually leading to cancer.

Within lung cancer, there are a few different types of cancer, based on the kinds of cells that turn cancerous. These cells look different from one another under the microscope. The authors of the study focused on two types of non-small cell lung cancer (NSCLC): lung squamous cell carcinoma and lung adenocarcinoma.

Adenocarcinomas are the most common type of lung cancer, accounting for 40 percent of all cases. Adenocarcinoma is minimally associated with smoking. Squamous cell carcinomas account for 30 percent of all lung cancers. They are more strongly associated with cigarette smoking than any other type of NSCLC. LSCC cases have declined in recent years, while LADC cases continue to increase.

Several previous studies cited by the authors found that the decrease in LSCC cases worldwide and increase in LADC are most likely caused by a rise in air pollution. However, these studies did not look at data across several years around the world. Because of this gap in knowledge, the study authors investigated how air pollution affects the number of LSCC and LADC cases in several different countries.

Rise in LADC Cases May Correlate With Increase in Air Pollution

For the study, the authors used data from lung cancer cases collected between 1990 and 2012 from the World Health Organization GLOBOCAN database, covering 36 countries in total. Air quality and smoking data was also analyzed alongside the number of LSCC and LADC cases over the years to make comparisons.

The study authors found that LSCC cases decreased between 1990 and 2012. This trend was driven by the decreasing cases in men. For women, there was no significant change. On the other hand, LADC cases continued to rise over the years, especially in women.

Notably, rates of smoking around the world have been on a downward trend. The study found that between 1990 and 2012, the rate dropped by 0.26 percent per year. In the United States, smoking rates declined at a rate of 0.40 percent per year.

These authors also concluded that rates of LADC appear to correlate with rising levels of air pollution, especially levels of black carbon (BC). BC may contain cancer-causing substances. Burning fossil fuels is one of the biggest contributors to this form of pollution.

The authors note that their study has some limitations — the data only goes to 2012, because recent data on cancer rates is not yet available. This study does not include the world’s two most populated countries, China and India — both of which have high levels of air pollution.