Application of the IASLC/ATS/ERS Classification of Lung Adenocarcinomas and Implications for Tumor Grading
Lauren Xu, Thomas Huebner, Fabio Tavora, Allen Burke. University of Maryland Medical Center, Baltimore, MD; Messejana Heart and Lung Hospital, Fortaleza, CE, Brazil
Background: The International Association for the Study of Lung Cancer (IASLC) in association with the American Thoracic Society and European Respiratory Society has recently re-classified adenocarcinomas of the lung based on histological patterns. However, there is lack of consensus about a grading system for these tumors. We studied a series of invasive lung adenocarcinomas and correlated the revised classification system with histologic features and metastatic potential to identify features relevant to grading.
Design: A series of invasive lung carcinomas resected over a 5-year period were retrospectively reviewed and classified by the new IASLC system. Proportion of each histologic subtype was estimated at 5% increments. Tumors with clinical and pathologic staging were included. 15 histologic parameters were blindly recorded and subsequently correlated with lymph node and distant metastasis.
Results: There were 125 patients 61 men (66 ± 8 years) and 64 women (65 ± 11 years). Tumors were reclassified by predominant pattern as lepidic predominant (LPA) (n=9), acinar (n=71), solid (n=21), papillary (n=11), and mucinous (n=13). Rate of lymph node metastasis was greatest in the solid type (p=.02). Rate of distant metastasis was greatest in the mucinous and solid groups (p<.02). Features associated with metastasis in the acinar group included predominant cribriform pattern (P=.03), prominent nucleoli (p=.05), solid or micropapillary areas <20% (p=.01), mitotic activity > 5/10 high power field (hpf) (p=.005) and lymphovascular invasion (p=.005); the latter 3 were independently significant when adjusted for tumor size. A 3 tiered grading system was devised with LPA, papillary, and acinar tumors as well differentiated, mucinous tumors moderately differentiated, and solid tumors poorly differentiated. Furthermore, solid growth <20%, lymphovascular invasion, or mitotic activity >5/10 hpf increased LPA, papillary, acinar, and mucinous tumors up one grade. Using this system, there was a stepwise increase in rate of lymph node metastasis (p<.0001) and distant metastasis (p=.0004) from well, moderately, to poorly differentiated tumors, which numbered 38, 45, and 42, respectively.
Conclusions: Application of the IASLC classification in this series resulted in a predominance of acinar adenocarcinomas. In order to stratify tumors into clinically relevant grades, additional histologic features of increased mitotic rate, lymphovascular invasion, and non-predominant areas of solid growth are useful.
Monday, March 4, 2013 9:30 AM
Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 296, Monday Morning