P3.04-016 Surgical Implications of the New Lung Adenocarcinoma Classification - Usefulness for Selecting Cases Undergoing Sublobar Resection: Topic: Miscellaneous I

Abstract

The 2015 World Health Organization (WHO) Classification of Lung Tumors has just been published and it confirmed a new adenocarcinoma classification based on histomorphologic subtype. We evaluated an appropriateness of new classification in a series in our institute and whether the classification could be useful for selecting limited cases undergoing sublobar resection. We retrospectively reviewed clinical records of all patients operated on for non-small cell lung cancer from 1997 to 2014 (n=1059). 382 patients (36.1%) had pathological stage IA adenocarcinoma of the lung classified. Pathologists performed histopathologic subtyping according to new 2015 WHO classification. Statistical analyses were made including Kaplan–Meier and Cox regression. Three overall prognostic groups were identified: low grade: adenocarcinoma in situ (AIS, n=115, 30.1%) and minimally invasive adenocarcinoma (MIA, n=37, 9.7%) had 97.5% and 96.9% of disease-free survival at 5 years (DFS, median follow-up was 72 months); intermediate grade: non-mucinous lepidic adenocarcinoma (n=72, 18.8%), acinar adenocarcinoma (n=72, 18.8%), and papillary adenocarcinoma (n=56, 14.7%), with 84.5%, 83.8%, and 63.1% of DFS; and high grade: invasive mucinous adenocarcinoma (n=11, 2.9%), solid adenocarcinoma (n=14, 3.7%) and micropapillary adenocarcinoma (n=5, 1.3%), with 81.5% of DFS. DFS in low grade was significant better than in other two grades (P<.001), however, there was no significant difference between in intermediate and high grade groups. The recurrent cases in MIA, lepidic, and acinar adenocarcinomas were probably observed papillary component. Preoperative imaging examinations such as consolidation/tumor (C/T) ratio on high resolution CT and maximum standardized uptake value (SUVmax) by FDG-PET were correlated with histopathologic grade according to new classification (P<.05). Moreover, sublobar resection was undergone for 195 cases (51.0%), more cases had been identified small tumor, low C/T ration, low SUVmax, and low grade subtypes, and DFS in sublobar resection was 93.2% which was significant better than in lobectomy (79.5%, P=.0034). Most of subtypes correlated with DFS, except of papillary adenocarcinoma and subtypes in high grade clinical aggressiveness, which may need more clinical investigation. As papillary components were observed in many recurrent cases, papillary is potentially higher malignancy and could be classified into high grade. Patients in low grade subtypes who underwent sublobar resection had better DFS, which can be predicted using tumor size and preoperative imaging examinations such as C/T ratio and SUVmax. So, the new classification has advantages for better selection of limited cases undergoing sublobar resection as a curative surgery.