The good news is that incidents of lung cancer have shown an overall decrease. The bad news is that some types of lung cancer are actually increasing.

The study, published in Cancer, shows that though the incidence rates are declining, some types such as adenocarcinoma are increasing. Additionally they found that the gender differences in incidents of lung cancer are decreasing.

Researchers at the US National Cancer Institute found that the overall rate of lung cancer has dropped by 12 percent.

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

Riedel Lewis said she thinks part of the reason for the decline is the decrease in smoking.

Between 90 and 95 percent of lung cancer is caused by smoking; since fewer people are smoking, this could cause changes in lung cancer rates.

One of the lung cancers on the rise, however, may be influenced by smoking as well. It is called adenocarcinoma. It accounts for 40 percent of all lung cancers, but it grows slower than other types of lung cancer and is therefore easier to control before it metastasizes.  

Dr. Norman Edelman, a senior medical advisor to the American Lung Association, said the increase in adenocarcinoma may be the result of people changing how they smoke. This could be because people are utilizing "light" cigarettes. They are inhaling more deeply.

"The deeper you breathe in smoke, the more likely the cancer-causing tars are going to get into the outer area of the lungs, and that's where adenocarcinoma starts," he said.

Another cancer that has scientists' attention hasn't been rising, but it has been dropping at a slower than normal rate. This cancer is called squamous cell carcinoma.

This cancer accounts for about 30 percent of lung cancers, Riedel Lewis said.  

Researchers found that the cancer rate in men has been dropping while the incidence rate in women has stayed the same, but according to Edelman, this is because women began smoking later than men.

He said ultimately, the fewer people who smoke will contribute to lung cancer rates also declining, so it's important to continue to inform people and encourage them not to smoke.