Tumor-infiltrating lymphocytes and pd-l1 expression in pre- and posttreatment breast cancers in the SWOG S0800 phase II neoadjuvant chemotherapy trial

Abstract

Our aim was to examine the association of pretreatment tumor-infiltrating lymphocyte (TIL) count and PD-L1 levels with pathologic complete response (pCR) and assess immune marker changes following treatment in tumor specimens from the S0800 clinical trial, which randomized patients to bevacizumab þ nab-paclitaxel, followed by doxorubicin/cyclophosphamide (AC) versus two control arms without bevacizumab (varying sequence of AC and nab-paclitaxel). TILs were assessed in 124 pre- and 62 posttreatment tissues (including 59 pairs). PD-L1 was assessed in 120 pre- and 43 posttreatment tissues (including 39 pairs) using the 22C3 antibody. Baseline and treatment-induced immune changes were correlated with pCR and survival using estrogen receptor (ER) and treatment-adjusted logistic and Cox regressions, respectively. At baseline, the mean TIL count was 17.4% (17% had zero TILs, 9% had 50% TILs). Posttreatment, mean TIL count decreased to 11% (5% had no TILs, 2% had >50% TILs). In paired samples, the mean TIL change was 15% decrease. Baseline PD-L1 was detected in 43% of cases (n ¼ 5 in tumor cells, n ¼ 29 stroma, n ¼ 18 tumor þ stroma). Posttreatment, PD-L1 expression was not significantly lower (33%). Higher baseline TIL count and PD-L1 positivity rate were associated with higher pCR rate even after adjustment for treatment and ER status (P ¼ 0.018). There was no association between TIL counts, PD-L1 expression, and survival due to few events. In conclusion, TIL counts, but not PD-L1 expression, decreased significantly after treatment. Continued PD-L1 expression in some residual cancers raises the possibility that adjuvant immune checkpoint inhibitor therapy could improve survival in this patient population.