CT Screening Identifying Slow-Growing Lung Cancers

One-quarter of lung cancers found through CT screening are slow-growing or indolent, many of which may have been overdiagnosed, according to findings of a study published in the December 4 issue of Annals of Internal Medicine. 

Researchers in Italy investigated whether lung cancer is potentially being over diagnosed, resulting in overtreatment. They conducted a retrospective analysis of 175 patients who had been diagnosed with primary lung cancer. Fifty-five patients had been diagnosed at baseline and 120 later on. The patients were followed for five years.

The researchers measured volume-doubling time (VDT) on low-dose CT (LDCT). This would determine the growth rate; tumors were deemed fast growing (fewer than 400 days), slow-growing (between 400 and 599 days) or indolent (600 days or longer).

Subjects who were found to have nodules that were 5 mm to 8 mm in diameter were rescreened after three months and those who had nodules that were 5 mm or smaller were rescanned after a year. PET/CTs were performed on most subjects who had noncalcified nodules that were larger than 8 mm. Subjects with nodules that were growing or were positive as per PET/CT underwent surgical biopsy and other interventions.

The results showed that among the 120 subjects who were diagnosed later, 19 (15.8 percent) were not visible on earlier scans and their tumors were fast growing, with a median VDT of 52 days. One hundred one subjects (84.2 percent) were progressive, including 70 fast-growing and 31 slow-growing or indolent cancers. Mortality due to lung cancer was significantly higher by 9.2 percent among the subjects with new compared with slow-growing or indolent cancer.
Overall mean VDT for fast-growing cancers was 223 days and for slow-growing or indolent cancers, 545 days.

The authors concluded that while the study was limited because VDT can only indicate overdiagnosis and was estimated for new cancer from one measurement (a diameter of 2 mm assumed the previous year), their findings did indicate that “slow-growing or indolent cancer comprised approximately 25 percent of incident cases, many of which may have been overdiagnosed.” They suggested that overtreatment of these cases could be limited by use of minimally invasive limited resection and nonsurgical treatments.