Clinicopathological Characteristics of Subcentimeter Adenocarcinomas of the Lung.
Fumiaki Kato, Makoto Hamasaki, Akinori Iwasaki, Hiroshi Iwasaki, Kazuki Nabeshima. Fukuoka University Hospital and School of Medicine, Japan
Background: The number of pT1a (≤2 cm in diameter) lung adenocarcinomas, especially of subcentimeter ones, is increasing because of recent development in radiographic techniques. In the current classification, pT1a tumors with a pure lepidic growth pattern (bronchioloalveolar carcinoma, BAC) have excellent prognosis, whereas invasive pT1a carcinomas can lead to recurrence or metastasis in spite of their small sizes. Thus, an accurate pathological diagnosis is critical. The aim of this study was to examine clinicopathological characteristics of subcentimeter adenocarcinomas, which helps in diagnosis of early invasive carcinomas.
Design: We retrospectively reviewed 595 adenocarcinomas resected in 2003-2009 at Fukuoka University Hospital, and analyzed 67 carcinomas that were ≤10 mm in diameter with reference to early invasive features. Invasion was diagnosed when it was associated with reactive fibroblastic proliferation, destruction of elastic fiber frameworks (detected using EvG stain), and discontinuity of subepithelial myofibroblastic layers (using α-SMA immunostaining). We regarded localized fibrous area more than 1 mm in diameter as minute scar (scar).
Results: Of the 67 cases, 38 (56.7%) were invasive and 29 (43.3%) were noninvasive (BAC). BAC and minimally invasive carcinomas (BAC>90%) comprised 48% of all tumors. Invasive carcinomas were significantly more frequent in male than female, and included 32 cases with BAC, and 6 cases without BAC (whole invasive). Moreover, a half of invasive carcinomas had no scar, in which cases we often had difficulty in detection of invasion without EvG stain and α-SMA immunostaining. However, high grade nuclear atypia was always associated with invasive carcinomas and helped in the diagnosis. Compared with adenocarcinomas of 11-20 mm in diameter, those of ≤10 mm included significantly more BAC and less whole invasive carcinomas. Invasive carcinomas with scar or micropapillary pattern were also significantly less.
Conclusions: Being familiar with histopathological characteristics of subcentimeter adenocarcinomas helps in accurate diagnosis of early invasive carcinomas. Moreover, EvG stain and α-SMA immunostaining are useful adjuncts to detect stromal invasion without scar.
Tuesday, March 1, 2011 1:00 PM
Poster Session IV # 270, Tuesday Afternoon