Prognostic Impact of Histopathologic Features in Pulmonary Invasive Mucinous Adenocarcinomas

Objectives: The prognostic significance of pathologic features and invasive size has not been well studied for invasive mucinous adenocarcinoma (IMA). This study evaluates the significance of pathologic features and invasive size in relation to clinical outcome. Methods: We reviewed the pathologic features in 84 IMAs, including histologic pattern, nuclear atypia, mitosis, necrosis, and lymphovascular invasion. The invasive size was calculated from the total size using the percentage of invasive components. Cases were subdivided into two pathologic grades based on five pathologic features, and the pathologic grade and adjusted T (aT) stage were correlated with disease-free and overall survival (OS). Results: Necrosis and N stage were significantly associated with aT stage, and a significant association was noted between OS and aT stage. Nuclear atypia, mitosis, and lymphovascular and pleural invasion also showed a significant association with OS. High-grade tumors showing a significantly worse OS compared with low-grade tumors, as well as pathologic grade (hazard ratio [HR],2.337; P=.043) and aT stage (HR,1.875; P=.003), were independent prognostic factors in multivariate analysis. Conclusions: The pathologic grading system stratified IMAs into high- and low-grade tumors with significant differences in OS. Invasive size may provide a better prognostic stratification for OS.