Prognosis of the second predominant subtype in lung adenocarcinoma: a retrospective single-center cohort study

BACKGROUND: The histologic classification of lung adenocarcinoma (LUAD) was mainly divided into three pathological subtype groups: the low-grade predominant subtype group (lepidic), the intermediate-grade predominant subtype group (papillary and acinar), and the high-grade predominant subtype group (micropapillary and solid). Previous studies have focused on the prognostic impact of predominant subtypes of lung adenocarcinoma. In this investigation, we investigated the effect of the second predominant subtype on prognosis. METHODS: The data of LUAD postoperative patients were retrospectively collected. Exclusion criteria included cases in which the pathologic results revealed a single characteristic, the presence of invasive mucinous LUAD, or if the first predominant and the second predominant groups could not be distinguished. Categorical variables were compared with the two-tailed Pearson χ(2) test and continuous variables with the Student’s t-test. Follow-up was conducted by telephone and other methods. Independent prognostic factors of the second major subtype were determined by the Kaplan-Meier method and log-rank test. The Cox proportional risk regression model was used to analyze the possible prognostic factors. RESULTS: Among 293 patients, the mean age was 61.9 years and 47.1% were male. The results revealed that when the predominant group was the low-grade group, the second predominant groups had no significant influence on overall survival (OS) (P=0.15) but significantly influenced disease free survival (DFS) (P=0.037). Subsequently, when the predominant group was the intermediate-grade group, the second predominant groups significantly influenced OS (P=0.024) but had no significant influence on DFS (P=0.3). Moreover, when the predominant group was the high-grade group, the second predominant groups significantly influenced OS (P=0.033) but had no significant influence on DFS (P=0.31). CONCLUSIONS: The independent prognostic effect of the second predominant group was not identified for OS and DFS of lung adenocarcinoma. The effects of the second predominant subtype groups on OS and DFS were not evenly distributed among different predominant subtype groups, and the low-grade second predominant subtype exhibited some protective effects on the middle-grade predominant subtypes.