GENEVA (FRONTLINE MEDICAL NEWS) – A lung-cancer screening CT interval of once-yearly for men and once every 3 years for women appears to be the optimum schedule for detecting most early-stage lung cancers while minimizing radiation exposure, results of a retrospective study suggest.

Among 96 patients (85 men and 11 women) with lung cancers detected on follow-up screening CT, the mean interval time between initial CT and diagnostic CT was significantly longer among women than among men, at 5.6 vs. 3.6 years (P = .02), reported Mi-Young Kim, MD, a radiologist at Asan Medical Center in Seoul, South Korea.

Men tended to have a higher stage at diagnosis, however. Stage I cancers were diagnosed in 82% of women, but only 49% of men. Tumor size was also larger among men at presentation at a mean of 29.5 mm vs. 15.5 mm, Dr. Kim and her colleagues found.

Current lung cancer screening guidelines vary somewhat, but most recommend annual screening for people aged 55-80 years who have a 30 pack-year or greater smoking history and are current smokers or have quit within the last 15 years.

Prior studies to see whether longer screening intervals were safe have yielded mixed results, possibly because of differences in clinical and radiologic presentation between men and women, Dr. Kim said.

To explore sex differences in lung cancer at the time of diagnosis, she and her colleagues retrospectively reviewed records for 46,766 patients who underwent screening at their center from January 2000 through February 2016, during which time, 282 patients were diagnosed with lung cancer. Of this group, 186 were diagnosed from the initial screening CT scan, and 96 – the cohort included in the study – were diagnosed from subsequent scans.

The authors found that the majority of men (72%) had solid nodules as the primary pathology. In contrast, ground-glass opacities were the most common nodular finding among women, occurring in 45% of the cases. The most common histology among men was adenocarcinoma (42%), followed by squamous-cell carcinoma (35%), small cell lung cancer (18%), and others (5%). All women presented with adenocarcinoma histology.

“Because ground-glass opacity nodule is the most common feature of lung cancer in women, and all cases are adenocarcinoma, the growth rate of cancers might be low,” Dr. Kim said in a statement.

Only 2 of the 11 women in the study were smokers, compared with 74 of the 85 men.

Looking at the operability of lung cancer according to screening intervals, the investigators found that 100% of tumors detected at 1 year in men were operable, compared with 94% of those detected at 2 years, and 55% for those detected at the 3-year interval. In contrast, among women, there were no tumors detected at 1 year, one operable tumor and no inoperable tumors at 2 years, and two operable and no inoperable tumors at 3 years. Beyond 3 years, however, the rate of inoperable tumors at the time of diagnosis was 32% in men and 25% in women.

“We included all patients screened for lung cancer in a 17-year period, but the number of women patients was low and further studies are needed to confirm the sex differences we found,” Dr. Kim acknowledged.

In a poster discussion session, Paolo Boffetta, MD, MPH , from the Icahn School of Medicine at Mount Sinai, New York, the invited discussant, commented that “I don’t think the main determinant of risk was adjusted for, which is smoking.”

“Only when this is adjusted for – when we compare smokers of the same pack-year history – then we can look at whether women and men do have different rates of appearance of nodules,” he said.

“To me, this is a very interesting suggestion that indeed the biology of the growth of these nodules may be different in men and women, but only if we are sure that the main environmental factor is taken care of.”

The study funding source was not disclosed.

Dr. Kim and Dr. Boffetta reported no relevant disclosures.