The findings of Dr. Denise Lewis and her colleagues at the National Cancer Institute (NCI) are published in CANCER, a peer-reviewed journal of the American Cancer Society (ACS).
According to the American Lung Association (ALA), lung cancer causes more deaths in the US than the next three most common cancers - breast, colorectal and pancreatic cancer - combined. In 2014, it is estimated that 159,260 Americans will die as a result of lung cancer.
Before the new research, it had been acknowledged that lung cancer incidence rates were falling across the US, but little was known about trends relating to the different subtypes of cancer, such as squamous and small cell carcinomas, or about different demographic groups.
Dr. Lewis and her colleagues have expanded the scope of previous analyses on lung cancer. Their study is an attempt to provide a clear picture of the state of lung cancer in the US in order to aid researchers in their monitoring of the population's lung health.
Decline in last 20 years
Deaths from lung cancer in 2014 are estimated to account for 27% of all cancer deaths in the US.
The research team analyzed data collected as part of the Surveillance, Epidemiology, and End Results (SEER) program, a source of population-based information that provides comprehensive data on cancer incidence and survival.
The aim of the study was to bring the classification of lung cancer subtypes up to date, as well as discovering the specific rates of the subtypes among different ethnic groups. Specifically, they examined the rates within white and black people in the US diagnosed from 1977-2010, and non-white Hispanic people, Asian/Pacific Islanders and white Hispanic people diagnosed from 1992-2010.
The researchers found that the rates of squamous and small cell carcinomas had fallen since the 1990s, at a much steeper rate in males than females. The rates for unspecified lung cancers also declined during this period.
The rates for adenocarcinomas were found to have decreased in males up until 2005, after which they rose quickly until 2010 among every racial, ethnic and gender group. Most recent rates for adenocarcinomas were higher in young females than among males in all demographic groups.
The researchers also found that the ratios of lung cancer rates for males and females declined more among black and white people than among other racial and ethnic groups.
Results 'reflect smoking history'
The authors suggest that changes in lung cancer rates reflect changes in the nation's smoking habits - in frequency, duration, cessation rates and the composition of cigarettes themselves, which could influence the levels of toxins that can make their way into the body. Dr. Lewis suggests that the results "can serve as a place marker for our population's changing lung exposures."
"All lung carcinoma histologies are associated with smoking," state the authors. The ALA identify that while around 90% of lung cancer cases can be directly attributable to smoking, other factors such as radon and occupational exposures identified as causing lung cancer are also associated with an increased risk caused by smoking.
The team concludes that the findings indicate the rates of lung cancer vary by subtype, ethnicity, gender, race and age. "It is important to monitor these changes as clinical cancer experts diagnose lung cancer and offer treatment based on specific characteristics of the cancer," says Dr. Lewis.
According to the researchers, with renewed clinical awareness and surveillance, their findings could guide future studies of cancer risk and control.
Recently, Medical News Today reported on a study that found almost 1 in 10 cancer survivors continues to smoke after their cancer diagnosis.