Impressive and durable response to nivolumab in a patient with metastatic type 2 papillary renal cell carcinoma: On-label but without evidence.

Nivolumab is a treatment option for patients with metastatic renal cell carcinoma (RCC) previously treated with targeted antiangiogenic therapy. Papillary renal cell carcinoma (PRCC) comprises 10-15% of RCC cases but non-clear cell subtypes were excluded from the immunotherapy trials. We report the case of a woman with recurrent metastatic PRCC who had an impressive therapeutic response to nivolumab with no significant adverse events. She had previously been treated with sunitinib and pazopanib with no response. She showed a remarkable clinical improvement after only the first 2 immunotherapy cycles and subsequent radiographic studies demonstrated a marked decrease in tumor burden. At present, she continues to show a durable benefit after 8 months of treatment. Her tumor had <1% positivity for PD-L1 staining and a low tumor mutational burden with no actionable mutations on genomic sequencing. Considering its high genetic variation, checkpoint blockade immunotherapies (CBIs) are attractive treatment options in PRCC. This is the third case that reports objective responses of nivolumab in PRCC. We believe our patient's experience supports the inclusion of non-clear cell RCC on clinical trials using CBIs. PD-L1 status and TMB may not serve as predictive biomarkers for response.