Should Pathologically Noninvasive Lung Adenocarcinoma Larger Than 3 cm Be Classified as T1a?

Adenocarcinoma in situ (AIS) is defined as noninvasive adenocarcinoma with a total tumor size including lepidic growth ≤3 cm; tumors >3 cm are classified as T1a. However, a tumor >3 cm that meets the histological criteria of AIS may have a prognosis equivalent to that of AIS. Here we examine the frequency and prognosis of noninvasive adenocarcinoma with a tumor >3 cm and the validity of the current definition of AIS tumor diameter.

The study was composed of patients with lung adenocarcinoma completely resected from January 2000 to December 2013 who met AIS histological criteria. Eligible patients were divided into 2 groups-the AIS group (tumor ≤3 cm) and the large AIS group (tumor >3 cm)-and the clinicopathologic characteristics and prognosis were retrospectively compared between the 2 groups.

A total of 277 patients were analyzed and large AIS was found in 7.9% (22) of the patients. The 5-year overall survival was 98.3% in the AIS group and 95.5% in the large AIS group. No patient had recurrence. The consolidation size from computed tomography and pathologic alveolar collapse size were both significantly larger in the large AIS group. No significant differences between groups were found in the consolidation-tumor ratio or in the ratio of the pathologic alveolar collapse size to the pathological total tumor size. The prognosis of patients with pathologically noninvasive adenocarcinoma >3 cm was comparable to that of AIS.

There is a possibility that tumor diameter need not be a consideration for AIS classification.