Clinicopathological characteristics of subcentimeter adenocarcinomas of the lung

Abstract

BackgroundIdentification of subcentimeter adenocarcinoma is becoming easier due to recent advances in radiographic techniques. Pathological (p) T1a (≤20mm) adenocarcinomas with a pure lepidic growth pattern have excellent prognosis, whereas invasive pT1a adenocarcinomas are associated with recurrence/metastasis despite their small size. Thus, an accurate pathological diagnosis is critical in such cases. This study examined the clinicopathological characteristics of subcentimeter adenocarcinomas, especially those associated with early invasive carcinomas. MethodsWe retrospectively reviewed 595 adenocarcinomas including 66 subcentimeter carcinomas, which were then analyzed with reference to early invasive features. ResultsOf the 66 subcentimeter tumors, 36 were invasive and 30 were noninvasive (adenocarcinoma in situ, AIS). Invasive carcinomas were significantly more frequent in males than females, and included 20 tumors with ≤5mm invasion in greatest dimension (minimally invasive adenocarcinoma, MIA) and 16 tumors with >5mm invasion, 5 of which had no lepidic growth portions (entirely invasive carcinoma). Approximately half of the invasive carcinomas had no localized fibrous area ≥1mm in diameter (LFA), and showed histological features of invasive carcinoma with localized lepidic growth including MIA (Noguchi's type C). Invasion was sometimes difficult to detect in these carcinomas. High-grade nuclear atypia was always associated with invasive carcinomas and aided the diagnosis. Moreover, invasive carcinoma with >5mm invasion was significantly associated with presence of metastasis in sensitivity analysis in patients followed for more than two years. Compared with adenocarcinomas of 11–20mm in diameter, subcentimeter carcinomas included significantly more AIS, fewer entirely invasive carcinomas, and fewer invasive carcinomas with LFA. ConclusionsFamiliarity with the histopathological characteristics of subcentimeter adenocarcinomas as described above could aid the accurate diagnosis of early invasive carcinomas.