Hatch, Ace J.

Colorectal cancer (CRC) is the third most frequent neoplastic disorder and is a main cause of tumor-related mortality, as many patients progress to stage IV metastatic CRC. Standard care consists of combination chemotherapy (FOLFIRI or FOLFOX). Patients with WT KRAS typing are eligible to receive anti-EGFR therapy combined with chemotherapy. Unfortunately, predicting efficacy of CRC anti-EGFR therapy has remained challenging. Here we uncovered that the EGFR pathway component RasGRP1 acts as a CRC tumor suppressor in the context of aberrant Wnt signaling. We found that RasGRP1 suppresses EGF-driven proliferation of colonic epithelial organoids. Having established that RasGRP1 dosage levels impact biology, we next focused on CRC patients. Mining 5 different data platforms, we establish that RasGRP1 expression levels decrease with CRC progression and predict poor clinical outcome of patients. Last, deletion of 1 or 2 Rasgrp1 alleles made CRC spheroids more susceptible to EGFR inhibition. Retrospective analysis of the CALGB 80203 clinical trial showed that addition of anti-EGFR therapy to chemotherapy significantly improved outcome for CRC patients when tumors expressed low levels of RasGRP1 suppressor. In sum, our data support RasGRP1 as a biomarker in the EGFR pathway that has potential relevance to anti-EGFR therapy for CRC patients.

588 Background: CALGB/SWOG 80405 found no difference in overall survival (OS) or progression-free survival (PFS) in 1137 patients with KRAS wild-type metastatic colorectal cancer (mCRC) treated with either the anti-VEGF agent bevacizumab (Bev) or the anti-EGFR agent cetuximab (Cet) in combination with chemotherapy (FOLFOX or FOLFIRI) as first-line therapy. Additional molecular biomarkers are required for the optimization of treatment choices for patients with mCRC. Methods: Levels of 24 proteins were assayed in EDTA-plasma samples using multiplex ELISA techniques. Plasma samples were collected at baseline and cycle 2 day 1 (C2D1). Analyses of baseline markers have been presented previously. Changes from baseline to C2D1 were expressed as an L-ratio (LR, log2 of C2D1 divided by baseline measure). LRs dichotomized at 0 were analyzed for potential prognostic and predictive effects on OS and PFS using Cox models while adjusting for confounders (post-hoc optimized cutpoints were used for PLGF, TIMP1, VCAM1, and VEGFR3 due to skew in the distributions of these markers). P-values are not corrected for multiple testing. Results: Baseline and matched C2D1 samples from 446 patients (212 Bev/234 Cet) were available for analysis. Thirteen markers were differentially modulated between arms (p < 0.05). Early increases in CD73 (p = 0.001), ICAM1 (p = 0.022), TIMP1 (p = 0.001), TSP2 (p = 0.024), and VEGFR3 (p = 0.006) were prognostic for shorter OS. Increases in ICAM1 (p = 0.008), TIMP1 (p = 0.042), and TGFB1 (p = 0.039) were prognostic for shorter PFS. Changes in VEGFR3 (pint = 0.097) and TGFBR3 (pint = 0.052) were predictive for OS and PFS, respectively. No other markers were predictive for OS or PFS (p < 0.1). Conclusions: Changes in circulating plasma protein biomarkers observed in patients enrolled in CALGB/SWOG 80405 were both prognostic and predictive for OS and PFS and warrant further study. Such changes could provide valuable information and help guide treatment decisions. Support: U10CA180821, U10CA180882, U10CA180888, U10CA180830; ClinicalTrials.gov: NCT00265850. [Table: see text]