Immunophenotype and Response to Immunotherapy of RET-Rearranged Lung Cancers.

RET rearrangements are identified in 1% to 2% of non-small-cell lung cancers (NSCLCs).1,2 In patients with advanced, RET-rearranged lung cancers, systemic therapy can be highly active. We demonstrated previously that pemetrexed-based chemotherapy can achieve an objective response rate of 45% and a median progression-free survival (PFS) of 19 months.3 Furthermore, the activity of targeted therapy has improved dramatically with the introduction of selective RET inhibitors to the clinic. In early-phase testing, objective response rates with LOXO-2924 and BLU-6675 are 68% (26 of 38) and 50% (seven of 14), respectively. These outcomes exceed the modest activity observed previously with multikinase inhibitors such as cabozantinib6 and vandetanib.7 In contrast, the activity of immunotherapy in RET-rearranged lung cancers has not been well characterized. This represents a clear unmet need, given that all prior regulatory approvals of immune checkpoint inhibitors, either alone or in combination with chemotherapy, and in stage III or IV disease, have technically included patients with RET-rearranged lung cancers.8,9 Furthermore, although increasing levels of programmed death-ligand 1 (PD-L1) expression and high tumor mutational burden (TMB) have been associated with benefit from immune checkpoint blockade,10 the immunophenotype of RET-rearranged lung cancers and the role of PD-L1 and TMB status in relation to benefit with immunotherapy remain poorly described. We set out to characterize these factors.