CCR5 Δ32 mutation and gene expression to predict outcome in patients (pts) with metastatic colorectal cancer (mCRC): Data from FIRE-3 and MAVERICC phase III trials

170 Background: Germline polymorphisms in CCR5 have been associated with treatment outcome in pts with mCRC receiving regorafenib and cetuximab-based treatment. CCR5 Δ32, a loss of function deletion, plays a key role in infectious diseases but data in CRC are scarce. We tested whether CCR Δ32 and CCR5 gene expression may be associated with outcome in mCRC pts receiving first-line treatment. Methods: The impact of CCR5 Δ32 was evaluated in 614 pts enrolled in the randomized FIRE-3 trial (FOLFIRI/cetuximab, cet, n = 313; FOLFIRI/bevacizumab, bev, n = 301). Gene expression was evaluated in 102 pts in the FOLFIRI/cet arm from FIRE-3 and 155 pts treated in the MAVERICC trial (FOLFIRI/bev, n = 76; FOLFOX6/bev, n = 79) from tumor tissue by HTG EdgeSeq Oncology Biomarker Panel and NanoString expression panel, respectively. The association between CCR5 Δ32 and clinical outcomes was evaluated using Cox regression and log-rank tests. Gene expression was dichotomized using an optimal cutoff and P-values computed using a permutation-based approach. Results: In FIRE-3, CCR5 Δ32 was significantly associated with worse PFS in patients with right-sided tumors (RT) receiving FOLFIRI/cet (n = 32; median PFS 3.41 vs 7.84 mo; HR 4.39, 95%CI 1.12-17.24; P= .022;). These associations were not observed in left-sided tumors or pts treated with bev. Lower levels of CCR5 expression trended to be associated with shorter PFS and OS in the same subgroup of RT treated in the cet arm ( P= .096 and P= .063 for PFS and OS, respectively). Lower CCR5 expression was associated with longer PFS in pts treated with FOLFIRI/bev in the MAVERICC trial, regardless of tumor side (mPFS 17.91 vs 11.04 mo; P= .03). A significant interaction between the impact of CCR5 expression levels on PFS and chemotherapy backbone was observed ( P= .019). Low CCR5 expression was associated with worse PFS in pts with RT treated with oxaliplatin (11.10 vs 13.80 mo; P= 0.023). Conclusions: Our results provide the first evidence that CCR5 Δ32 and CCR5 gene expression levels may predict outcomes in mCRC pts receiving first-line treatment with a differential effect depending on tumor location, biologic agent and chemotherapy backbone.