RET Rearrangement as a Predictor of Unresponsiveness to Immunotherapy in Non-Small Cell Lung Cancer: Report of Two Cases with Review of the Literature.

Patients with epidermal growth factor receptor and anaplastic lymphoma kinase positive non-small cell lung cancer (NSCLC) generally respond poorly to treatment with immune checkpoint inhibitors such as anti-programmed cell death-1 (PD-1) or anti-programmed cell death ligand-1 (PD-L1) given with or without anti-cytotoxic T lymphocyte antigen-4 (CTLA-4) drugs. However, the efficacy of immunotherapy in patients with oncogene-addicted NSCLC harboring minor drivers, such as fusions in the rearranged during transfection (RET) gene, is still unclear. Here we describe two patients with RET-positive advanced NSCLC with PD-L1 expression ≥ 50% who developed progressive disease during first-line treatment with the anti-PD-1 agent pembrolizumab. In particular, while patient 2 was immediately switched to treatment with a selective RET inhibitor within the setting of a clinical trial, patient 1 responded to cytotoxic chemotherapy delivered at the time of progression while on pembrolizumab. These cases of NSCLC are discussed in the context of current literature, which seems to support our observation that patients with RET-positive NSCLC are unlikely to benefit from immunotherapy. Therefore, we suggest that for RET-positive patients with PD-L1 ≥ 50%, consideration should be given to upfront treatment approaches other than single-agent immunotherapy, namely selective RET inhibitors (if available) or regimens including cytotoxic chemotherapy.