RSNA: CT screening significantly reduces lung cancer mortality

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CHICAGO--CT screening can significantly reduce lung cancer mortality, according to a paper presented Tuesday at the annual meeting of the Radiological Society of North America (RSNA).

According to Claudia Henschke, MD, PhD, professor of radiology at New York Presbyterian Hospital–Weill Cornell Medical Center in New York City, while lung cancer screening has been shown to increase lung cancer curability by 80 percent, as estimated by long-term Kaplan-Meier survival rate, the current study is meant to assess the reduction in long-term lung cancer mortality.

“Clearly there’s a relationship between the two, but it’s a complex relationship,” said Henschke.

The researchers compared lung cancer mortality in a group of 8,000 smokers--not exposed to asbestos and averaging 66 years in age—who had baseline CT screening for cancer in New York to an unscreened cohort of 308,000 smokers (average 58 years of age) who were enrolled in the American Cancer Society Prevention Study II (CPS-II). The New York group was older, had a history of heavier smoking, had started smoking at an earlier stage, but had fewer participants who were current smokers.

The researchers determined the actual observed deaths in the screened cohort and then obtained actual mortality rates in the unscreened group and used those actual mortality rates to determine the number of deaths that would have been expected in the screened cohort.

The researchers identified 64 deaths in the New York group, 39 of which were from lung cancer diagnosed by screening. Four of the participants who died had an interim diagnosis of lung cancer and 21 were participants who discontinued screening for 19 months or more and died 19 to 93 months (median 51 months) after their last negative scan. Using the CPS-II study as a model, the researchers determined that there should have been 99.8 expected deaths in the screened group—so there was a 36 percent mortality reduction in the New York group.

“If you look at it over time, you see that initially the two cohorts would be the same,” said Henschke. “And then at a point, the screened cohort's deaths start to decrease and at some later point--because basically screening was done for only two rounds in this cohort—the deaths again start and then parallel. So mortality reduction only becomes evident after three or four years from initial enrollment, and that’s why you need to focus on the interval during which the mortality reduction becomes evident. And when screening is not continuous the mortality rate starts increasing again.”

According to Henschke, any bias that might have affected the results, such as the potential for radon exposure in New York, would have resulted in underestimating rather than overestimating the actual mortality reduction. “In other words, it might be even larger than what is seen in this analysis,” she said.

Henschke concluded that while CT screening significantly reduces lung cancer mortality, “it needs to be understood that to have a mortality reduction screening must be continuous."