Lung cancers diagnosed in annual repeat rounds of CT screening are similar—in volume doubling time and cell-type distribution—to those detected in the absence of screening, according to a study published online March 27 in Radiology.

Growth rates of lung cancers found by annual rounds of CT screening are important for determining the usefulness and frequency of screening, as well as for determining treatment. “There was concern that cancers diagnosed in the screening context were somehow different than cancers found in routine practice, that they were not aggressive,” Claudia I. Henschke, PhD, MD, professor of radiology at Mount Sinai School of Medicine in New York City and International Early Lung Cancer Action Program (I-ELCAP) principal investigator, said in a statement.

Henschke and colleagues sought to determine the distribution of volume doubling time (VDT) of lung cancers diagnosed in repeat annual rounds of CT screening with respect to tumor growth and cell types.

The researchers identified all first diagnoses of primary lung cancer after a negative screening result seven to 18 months earlier in the I-ELCAP database for 1993-2009. Henschke and colleagues identified 111 instances of first primary lung cancer diagnosed either through screening or between rounds after a negative result of the prior screening seven to 18 months earlier. Of the 111 cancers identified, 88 were clinical Stage I. The investigators then analyzed VDT and cell-type distribution.

They estimated the VDT by calculating length and width of each cancer upon identification and at the most recent prior screening.    

The results showed that the median volume doubling time was 98 days.  Most of the cancers, 99 of the 111, manifested as solid nodules, while 12 cancers manifested as sub-solid nodules. Solid nodule cancers had significantly faster volume doubling times than sub-solid nodule cancers.  According to Henschke, identifying the VDTs for specific lesion types may lead to more tailored treatment.

Given the difference in the growth rates of cancers in solid and sub-solid lesions and that the sub-solid ones tend to be less aggressive than solid ones, “a less aggressive approach is indicated for both diagnosis and treatment of sub-solid lesions,” Henschke said.

VDTs for lung cancers diagnosed in clinical practice in the absence of screening have been reported to range from 20 to 360 days. A recent study, based on a systematic medical literature review, reported a mean VDT of 135 days for non-small-cell lung cancers diagnosed in the absence of screening.

Also, the frequencies of small-cell carcinoma and adenocarcinoma among all lung cancers have been reported to be approximately 20 percent and 50 percent, respectively, in the absence of screening. In repeat rounds of CT screening, these frequencies were nearly identical (19 percent and 50 percent). 

“This study shows that the cell types of cancer diagnosed in annual rounds of screening, as well as their growth rates, are quite similar to those that are found in clinical practice where it is well understood that lung cancer is highly lethal,” Henschke said. The first round of screening for any cancer detects a higher proportion of slower-growing cancers than those detected in clinical practice, she noted. The subsequent, repeat rounds of screening, however, reflect what is found in clinical practice.

The findings refute two arguments about the lung cancers detected at CT screening. These are: screening detects slow-growing cancers that would not become life-threatening and life-threatening cancers are characterized by rapid growth that does not allow detection while curable.