[1641] Strong Correlation between Solid and Micropapillary Subtypes of Lung Adenocarcinoma (AD) in Primary and Metastatic Sites

G Sica, W Travis, A Moreira. Memorial Sloan Kettering Cancer Center, New York, NY

Background: AD mixed subtype, the most common histologic type of lung cancer, is a heterogeneous group composed of a mixture of different patterns and pattern combinations. The prognostic significance of each individual type of AD within the mixed subtype is not clearly understood. In this study, the predominant pattern of AD in the primary tumor is compared with the pattern seen in the metastatic site to determine whether the presence of a specific pattern in a mixed subtype tumor correlates with higher stage of disease.
Design: This is a retrospective study of 59 patients with mixed subtype ADs that presented with regional lymph node metastasis. Histologic subtyping was evaluated by comprehensive semiquantitation and classified by major subtype. The major subtypes were compared in the primary and the metastatic site.
Results: The patient's age ranged from 35 to 83 years (mean age of 65), 43 were women and 16 men. Acinar was the most common subtype, present in 100% of cases, followed by micropapillary (81%), papillary (78%), solid (60%) and bronchioloalveolar (18%). Acinar was the predominant pattern in 53% of the tumors, followed by papillary (20%), solid (17%), and micropapillary (10%). In contrast, the predominant metastatic pattern was solid (31%), acinar (27%), micropapillary (27%), and papillary (15%). The overall correlation coefficient between predominant pattern in the primary site and metastasis was of 0.489 (p <0.0001). In the cases that micropapillary (n=6) or solid (n=10) types were the predominant patterns in the primary tumor, the corresponding lymph node metastasis had the same pattern as the primary tumor. Even when the micropapillary or solid types comprised a minor, 5-10%, of a primary tumor, these types were more likely to be seen in the lymph node metastases.
Conclusions: AD classification using the most prominent subtyping reveals that when a mixed subtype AD contains either solid or micropapillary pattern, these patterns are overrepresented in the metastatic sites, a finding that correlates with the known high grade nature of these subtypes. A predominant acinar or papillary pattern in mixed subtype does not appear to correlate with the pattern in the metastatic site. Therefore, the high grade solid and micropapillary subtypes of AD are more likely to metastasize to lymph nodes even if they are not the most prominent subtype in the primary tumor.
Category: Pulmonary

Monday, March 9, 2009 11:00 AM

Platform Session: Section F, Monday Morning