Overall incidence rates for lung cancer are on the decline reveals a new study conducted by the National Cancer Institute (NCI).

Per the study, led by NIC's epidemiologist Denise Riedel Lewis, the lung cancer rate has seen a drop by nearly 12 percent. However, some types of lung cancer rates are on the rise.

"The good news is that lung cancer rates are declining. However, it's not as clear for certain subtypes, and we are not exactly sure of the reasons behind these increases," revealed Lewis.

The study analyzed the trends based on "histologic type and demographic characteristics." The researchers investigated lung cancer rates in the U.S. by analyzing data from 1977 to 2010 from NIC's Surveillance, Epidemiology, and End Results (SEER) program.

The data from this program comprised over 50,000 lung cancer cases and was collated with data from the census to get an estimation of the lung cancer rates for the U.S. The team of researchers also delved into the varied types of lung cancer, which include squamous cell, small cell and adenocarcinoma.

Lewis' team discovered that the lung cancer rates grew in the 1990s at an average of 62 cases per 100,000 person-years. In 2010, however, the rate of lung cancer began declining and slid to 53 cases per 100,000 person-years. Interestingly, the decline in lung cancer rate was slower for women when compared to men.

According to the researchers, smoking is the root cause for nearly 90 percent to 95 percent of lung cancer incidences. One reason contributing to the decline in lung cancer rates could be reduced smoking, which is linked to growing awareness among the younger population of cigarette smoking risks.

Moreover, several "smoke-free" zones have mushroomed across restaurants, offices and even beaches, which makes public smoking difficult. This in turn has led to people smoking less. Doctors are also of the opinion that exposure to chemicals and asbestos, which may have led to lung cancer, is also less.

However, adenocarcinoma, a type of lung cancer, is slowly seeing an increase and this may be owing to an increase in smoking. Adenocarcinoma, the researchers reveal, accounts for an alarming 40 percent of lung cancers. However, this type of lung cancer is easier to grapple with as it grows at a slower rate when compared to other lung cancers.

"These findings will require renewed clinical awareness and surveillance and will guide future studies of cancer risk and control," note the study authors.

The study has been published in the journal Cancer on August 11.

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