Endobronchial spread of adenocarcinoma is a distinct pattern of invasion and associated with inferior clinical outcomes in lung adenocarcinoma.

Aim: The spread of lung adenocarcinoma cells into the bronchi and bronchioles is not well documented. We termed this histological finding "endobronchial spreading of adenocarcinoma" (EBSA) and investigated its prevalence and clinical significance. Methods and Results: We reviewed 320 resected specimens from patients diagnosed with invasive adenocarcinoma, and EBSA was observed in 144 patients (45%). EBSA was significantly associated with advanced pathological stage, higher histological grade, larger tumour invasion, lymphovascular infiltration, and spread through air spaces. Patients with EBSA had significantly shorter relapse‐free survival (RFS) and cancer‐specific survival (CSS) in univariate analysis (P < 0.001). In a subgroup analysis of patient with small‐sized (invasion size ≤30 mm) adenocarcinoma in the localized stage, EBSA was an independent inferior prognostic indicator in multivariate analysis. In a subgroup analysis of patients with small‐sized Grade 1 nonmucinous adenocarcinoma (n = 61), EBSA was observed in 11 patients, and the presence of EBSA was associated with significantly shorter RFS and CSS (P = 0.026 and P = 0.001, respectively). Conclusion: Our results demonstrated that EBSA is a significant risk factor for disease recurrence and cancer‐related deaths. EBSA can be regarded as a distinctive pattern of invasion and its recognition can be beneficial in the diagnosis of lung adenocarcinoma. [ABSTRACT FROM AUTHOR]