Micropapillary and solid subtypes of invasive lung adenocarcinoma: Clinical predictors of histopathology and outcome

Objective: To evaluate the clinical effect of the presence of a micropapillary or solid subtype on the outcomes in lung adenocarcinoma and to determine the predictors of such a histopathologic diagnosis. Methods: A total of 511 patients with lung adenocarcinoma ≤3 cm were included. According to the presence of micropapillary or solid subtypes, we classified the patients into 4 subgroups: both subtypes absent (MP-/S-, n = 87), either subtype present (MP+/S-, n = 207 and MP-/S+, n = 196), and both present (MP+/S+, n = 21) to determine the association between the micropapillary or solid subtype and survival outcome or clinical and imaging conditions. Univariate and multivariate analyses were undertaken to determine the parameters, allowing the prediction of the presence of the micropapillary or solid subtype. Results: Overall survival (OS) and disease-free survival (DFS) differed significantly among the 4 subgroups (P <.001 and P =.004, respectively). The MP-/S- tumors showed better DFS than those containing either the micropapillary or solid subtype. Patients with the micropapillary subtype had significantly worse OS than patients without the micropapillary subtype. This difference remained significant, together with stage, after adjustment for gender, age, adjuvant therapy, tumor size, and solid subtype (DFS and OS, P =.016 and P =.002, respectively). On multivariate analysis, greater than stage I, tumor size ≥2.5 cm, solid mass, and maximal standardized uptake value of ≥7 were independent predictors of the presence of a micropapillary or solid subtype. Conclusions: Micropapillary and solid subtypes are common in tumors greater than stage I, with size ≥2.5 cm, pure solid type, and maximal standardized uptake value of ≥7, which were predictors for poor DFS. The presence of the micropapillary subtype was a single prognostic factor for OS.