Anti-EGFR therapy has the potential to increase antitumor immune responses. Therapeutic strategies targeting EGFR and immune checkpoints may benefit patients (pts) with mCRC. We conducted a phase Ib/II clinical trial of cetuximab with pembrolizumab in RAS wild-type (RASwt) mCRC; the primary efficacy results of the trial have been reported (Fountzilas et al ESMO GI 2020). Herein, we present correlative tissue analysis.
Tumor biopsies were obtained baseline (pre-Tx) and after 12 weeks (post-Tx); multiplex immunohistochemistry for PD-L1, T-cell exhaustion (TIM3, CTLA4, LAG3) and activation (OX40) markers was performed. T-cells were characterized as partially activated-1 (OX40+/PD-L1-, 1/3 exhaustion markers+); partially activated-2 (OX40+/PD-L1-, 2/3 exhaustion markers+); partially activated-3 (OX40+/PD-L1-, 3/3 exhaustion markers+); exhausted-1 (OX40-/PD-L1-, 1/3 exhaustion markers+); exhausted-2 (OX40-/PD-L1-, 2/3 exhaustion markers+); and exhausted-3 (OX40-/PD-L1-, 3/3 exhaustion markers+).
Forty-two pts were enrolled; 14 with matched pre-Tx and post-Tx biopsies, 24 with pre-Tx only. PD-L1 expression was higher in pre-Tx metastasis (M) vs. primary tumor (PT) in both tumor and stromal cells within the microenvironment (TME). The no. of activated T-cells was higher pre-Tx in PT compared to M. The no. of exhausted-2 T-cells in pre-Tx was higher in M vs. PT. The no. of activated T-cells and partially activated-1 T-cells was higher in post-Tx vs. pre-Tx M. There was no change in the no. of exhausted T-cells on post-Tx. PD-L1 decreased on tumor cells and increased in the TME on post-Tx.
Temporospatial heterogeneity in the immune landscape of the TME was evident in RASwt mCRC. With the limitation of small sample size, we observed increased PD-L1 expression and exhausted T-cells and decreased activated T-cells in M compared to PT. There was an increase in activated T-cells post-Tx, but the no. of exhausted T-cells was similar, potentially explaining the lack of additive benefit from pembrolizumab. Evaluating the PT in mCRC might not be reflective of immunosuppression in M. Combinations with mAb targeting other T-cell exhaustion pathways may be necessary to improve the antitumor efficacy of the EGFR-based regimens.
Clinical trial identification
Legal entity responsible for the study
Roswell Park Comprehensive Cancer Center.
Merck Sharp & Dohme Corp.
C. Fountzilas: Research grant/Funding (institution): Merck; Research grant/Funding (institution): National Comprehensive Cancer Network; Research grant/Funding (institution), free drug support: Pfizer. R. Iyer: Research grant/Funding (institution): Merck. All other authors have declared no conflicts of interest.