PD-L1 diagnostics in the neoadjuvant setting: implications of intratumoral heterogeneity of PD-L1 expression in triple negative breast cancer for assessment in small biopsies.

There is substantial heterogeneity of PD-L1 expression between small tissue samples from the same TNBC tumor, especially for IC expression. This poses challenges for evaluation of PD-L1 expression in the neoadjuvant setting. Negative biopsies should prompt further investigation, and multiple biopsies might be necessary.