The efficacy of pemetrexed-based chemotherapy in patients with advanced lung adenocarcinoma with novel ROS proto-oncogene 1, receptor tyrosine kinase gene (ROS1) oncogenic rearrangement is unclear. This study aimed to compare the efficacy of pemetrexed-based chemotherapy in patients with advanced ROS1-fusion lung adenocarcinoma with its efficacy in those having different driver mutations.

We retrospectively identified patients with advanced lung adenocarcinoma who were screened for epidermal growth factor receptor gene (EGFR) mutations, echinoderm microtubule associated protein like 4 gene (EML4)-anaplastic lymphoma receptor tyrosine kinase gene (ALK) translocation, Kirsten rat sarcoma viral oncogene homolog gene (KRAS) mutations, and ROS1 fusion by using multiplex reverse-transcriptase polymerase chain reaction. Patients who received pemetrexed-based therapy were enrolled for further analysis. The demographic data, clinical outcomes, and thymidylate synthase immunostaining (H-score) of patients with ROS1 fusion-positive lung adenocarcinomas were compared with those of patients harboring EGFR mutations, EML4-ALK fusion, KRAS mutations, and quadruple negativity.

A total of 253 patients with advanced lung adenocarcinoma received a pemetrexed-based regimen and were classified on the basis of molecular findings as follows: 102 patients (40.3%) with EGFR mutations, 32 patients (12.6%) with EML4-ALK translocation, three patients (1.2%) with KRAS mutations, 19 patients (7.5%) with ROS1 fusion, and 97 patients (38.3%) with quadruple-negative status. Patients with ROS1 fusion had a better overall response rate (57.9%, p = 0.026), disease control rate (89.5%, p = 0.033), and longer progression-free survival (7.5 months, p = 0.003) compared with patients harboring other driver mutations. However, the H-score of thymidylate synthase was not associated with the response to pemetrexed therapy in patients with different molecular subtypes of lung adenocarcinoma.

ROS1 fusion positivity is probably a favorable factor of pemetrexed-based therapy for patients with lung adenocarcinoma.