Association of PD-1 and PD-L1 protein expression in matched primary and metastatic renal cell carcinoma tumors.

418 Background: Therapy targeting programmed death (PD)-1 and PD-L1 proteins has activity in metastatic renal cell carcinoma (mRCC). Expression of these proteins on tumor and infiltrating immune cells is associated with a higher response to drugs inhibiting this pathway. However, these associations have been made based on primary tumor expression, while therapy is directed against metastatic deposits. Methods: Patients with mRCC and metastases (all clear cell; 3 with sarcomatoid changes) who had undergone resection of both the primary and at least one metastatic tumor were included. Samples were evaluated for PD-1 and PD-L1 expression by immunohistochemistry using anti-PD-1 clone NAT105 and Merck proprietary anti-PD-L1 clone 22C3. Stained sections were scored for PD-1 and PD-L1 using a semi-quantitative 0 to 5 scale (0 = negative, 1 = rare, 2 = low, 3 = moderate, 4= high, 5 = very high). PD-1 expression was limited to cells with lymphoid morphology, PD-L1 expression was evaluated for both tumor and non-tu...