Dako 22c3 antibody

Immunohistochemistry was performed on pretreatment tissue specimens to assess PD-L1 expression using the Dako 22C3 antibody (Agilent, Santa Clara, CA, USA). The TPS was used to measure results, as previously described (21 (link)) with cut points of < 1%, ≥ 1% to 49%, and ≥ 50%. Insufficient tissue and unknown PD-L1 status were included in the < 1% cut point category.

Patient tumor samples, provided as 10 unstained slides or 1 block of formalin-fixed paraffin embedded samples, were obtained for analysis from a biopsy of a tumor lesion not previously irradiated, and had to be obtained after the diagnosis of metastatic disease. PD-L1 membrane expression was obtained using the commercially available Dako 22C3 antibody (Agilent Technologies, California). The PD-L1 modified proportion score (MPS) was used: this score is used to evaluate mononuclear inflammatory cells (MICs) and tumor cells reactive for PD-L1 in relation to tumor cells. MICs in stroma and adjacent tissue were not included in the MPS.