Intraoperatively measured tumor size and frozen section results should be considered jointly to predict the final pathology for lung adenocarcinoma.

Invasive adenocarcinoma intraoperatively misdiagnosed as adenocarcinoma in situ or minimally invasive adenocarcinoma is more likely to undergo potentially insufficient resection. The purpose of our study was to evaluate the diagnostic accuracy of frozen section. We retrospectively reviewed 1,111 lung adenocarcinomas from January to March 2016 to evaluate the diagnostic performance of frozen section. A derivation cohort consisting of 436 cases of adenocarcinoma in situ or minimally invasive adenocarcinoma diagnosed by frozen section in the same period were analyzed to find predictive factors for invasive adenocarcinoma as the final diagnosis. Validation cohorts (first: April to June 2016, second: January to March 2015) were included to confirm the results. The overall concordance rate between frozen section and final diagnosis was 92%. Most frozen section errors were underestimation. The sensitivity of frozen section diagnosis for minimally invasive adenocarcinoma (74%) was significantly lower than others. Intraoperatively measured tumor size was the only independent factor for invasive adenocarcinoma as the final diagnosis (<1 cm: 2%, reference; 1-1.4 cm: 15%, odds ratio, 5.678; > 1.5 cm: 18%, odds ratio, 5.878; P = 0.001) in the derivation cohort, and was confirmed by validation cohorts. Fifty-nine misdiagnosed invasive adenocarcinomas in the three cohorts consisted of 54 lepidic predominant type, 1 papillary and 4 acinar predominant type. There were no positive N1, N2 node, pleural, lymphatic and vascular invasion cases found. Thirty-seven (37/59, 63%) cases of misdiagnosis were attributed to sampling error, which was the main reason. Our study suggests that adenocarcinoma in situ or minimally invasive adenocarcinoma ≥1 cm by frozen section were more likely to be invasive adenocarcinoma because of sampling error. Frozen section diagnosis of adenocarcinoma in situ or minimally invasive adenocarcinoma should be considered cautiously for tumors ≥1 cm to avoid potentially insufficient resection.