Optimal method for measuring invasive size that predicts survival in invasive mucinous adenocarcinoma of the lung

The purpose of this study was to determine the optimal method for measuring pathological invasive size that predicts prognosis in invasive mucinous adenocarcinoma (IMA). We analyzed patients who underwent complete surgical resection for lung IMA. The invasive size of IMA was measured using two methods: (1) excluding lepidic method (ELM), that is, lepidic component was excluded from the invasive area regardless of alveolar mucin and (2) including lepidic method (ILM), that is, lepidic component was included as invasive area if alveolar space was filled with mucin. The prognostic predictability of ELM and ILM on survival was assessed using univariable and multivariable Cox regression models. The discriminative power was assessed using concordance probability estimate (CPE) and Akaike’s information criteria (AIC), and the prognostic impact of the newly redefined pathological stage according to ELM or ILM was also assessed. A total of 101 patients were included. The median invasive size via ELM and ILM was 1.4 cm (range, 0.0–7.7 cm) and 2.1 cm (range, 0.0–14.2 cm), respectively. ELM had better discriminative power than ILM (ELM, HR = 1.38, AIC = 110.19, CPE = 0.671; ILM, HR = 1.19, AIC = 111.52, CPE = 0.655). Although the survival curves based on ILM crossed between T3 and T4, the overall survival (OS) curves based on ELM were sufficiently distinct from one another. ELM has higher discriminative power for OS, and thus the optimal method for measuring the pathological invasive size of IMA should exclude the lepidic component regardless of alveolar mucin.