Differences in patterns of recurrence of squamous cell carcinoma and adenocarcinoma after radiotherapy for stage III non-small cell lung cancer.

Purpose: To evaluate the differences in patterns of recurrence and treatment results by histology after definitive radiotherapy for stage III non-small cell lung cancer (NSCLC) in Japan.
Materials and Methods: Patients with stage III NSCLC who underwent definitive radiotherapy between 2000 and 2016 in our institution were included. A total of 217 patients were enrolled. Propensity score matching was used to exclude the following confounding factors: (1) age (≥70 years or <70 years), (2) gender, (3) T factor, (4) N factor, (5) Eastern Cooperative Oncology Group performance status score and (6) smoking status (Brinkman index ≥400 or <400).
Results: The median observation period for survivors was 55.1 months. After propensity score matching, the Sqcc and adenocarcinoma groups each included 62 paired patients. There was no significant difference in OS or PFS between the adenocarcinoma and Sqcc groups. However, rates of recurrence in the GTV-primary site (p = 0.009) and GTV-lymph node site (p = 0.037) were significantly higher in patients with Sqcc than in patients with adenocarcinoma. New metastatic recurrence was more frequent in patients with adenocarcinoma than in patients with Sqcc (p = 0.025).
Conclusion: There were significant differences in patterns of recurrence after definitive (chemo)radiotherapy between patients with Sqcc and patients with adenocarcinoma.