Correlation of histological components with tumor invasion in pulmonary adenocarcinoma

Pulmonary adenocarcinoma (PA) is the most common histologic type of primary lung cancer. Generally, adenocarcinoma was composed by five major components. The present study aimed to evaluate changes in the composition of adenocarcinoma components as the tumor grows; in addition, to analyze the correlation between the occupancy rates of histologic components of the tumor in regard to prognosis.

Pathologic data were retrospectively evaluated for 206 patients who underwent curative resection of PA. We investigated how histologic component occupancy rates changed as tumor size and N stage increased. To evaluate local invasiveness, the major components of the present group and absent group of pleural invasion, lymphatic invasion, and vascular invasion were compared.

The mean percentages of acinar and solid components significantly increased with an increase in size (P = 0.006, P < 0.001) ; however, the percentage of lepidic components decreased (P < 0.001). In cases with a solid component and a micropapillary component, a gradual increase was found with an increase N stage (P = 0.001, P < 0.001); however the percentage of lepidic components decreased (P < 0.001). Average differences of histologic components dependent upon whether pleural, lympathic and vascular invasion were present, the difference of micropapillary and lepidic components were statistically significant. With logistic regression analysis, as the occupancy rate of the lepidic component increased, the probability of pleural invasion, lymphatic invasion, and vascular invasion decreased; in cases with a micropapillary component, as the occupancy rate of increased, the probability of lymphatic invasion and vascular invasion increased. In multivariate analysis using the Cox propotional hazards model, the occupancy rates of acinar(p = 0.043; odds ratio = 1.023), micropapillary(p = 0.002; odds ratio = 1.051) and lepidic (p = 0.005; odds ratio = 0.966) components were significantly associated with recurrence.

The lower the occupancy rate of a lepidic component and the higher the occupancy rates of acinar, solid, and micropapillary components, the likelihood of tumor progression increased. In addition, as the occupancy rate of a lepidic component decreased and a micropapillary component increased, local invasiveness and recurrence rate increased; thus, increasing the probability of a poor prognosis.