Bertagnolli, Monica M.

638 Background: Colorectal cancer (CRC) is a heterogeneous disease with distinct molecular subtypes in part based on RAS mutational status. It is plausible that RAS mutations are differentially distributed between CC and AA and may contribute to poor outcomes in AAs with CRC. Methods: We did a retrospective analysis of CALGB/SWOG 80405 trial patients. We divided the entire cohort into 2 groups: a) Common RAS: mutation in KRAS exon 2, codon 12 or 13; b) Extended RAS: any NRAS mutations or mutation in KRAS except those listed above. We then analyzed these two subgroups for association between RAS mutations and race (3 categories: Caucasian, AA, Others) using chi-square test for univariate analyses and logistic regression for multivariate analysis. We also analyzed the effect of extended RAS testing on prognosis of metastatic CRC by estimating the overall survival (OS) using Kaplan-Meier method and 95% confidence interval (CI). Cox proportional-hazard model was used for multivariate analyses. Results: There were 1729 CRC patients in common RAS group of which 357 (20.6%) had mutations present. Extended RAS group had 621 patients of which 95 (15.5%) had mutations present. There was no significant difference in the rate of common RAS mutations between CC and AA (20.5% vs. 24%, p=0.22). However, extended RAS mutations were significantly more in AA as compared to CC (25% vs. 14%, p=0.02). Multivariate analysis adjusted for age, gender, prior adjuvant chemotherapy and pelvic radiation confirmed higher odds of extended RAS mutation in AA compared to CC (adjusted OR 1.12; 95% CI 1.01-1.23; p=0.02). The median OS in patients with an extended RAS mutation was shorter as compared to those without extended RAS mutation (25.3 vs. 31.9 months; HR 1.26; 95% CI 0.99-1.62; p=0.05). Multivariate analyses adjusted for age, gender, race, prior adjuvant chemotherapy and pelvic radiation showed a trend towards longer OS in patients without extended RAS mutation as compared those with extended RAS mutation (adjusted HR= 1.24, 95% CI, 0.97-0.1.58, p=0.08). Conclusions: Extended RAS mutations are significantly more common in AA as compared to CC. Additionally, presence of extended RAS mutation may confer a poor prognosis in CRC patients.

3511 Background: CALGB 80405 was a randomized Ph3 trial showing no OS or PFS difference in mCRC pts treated with Bevacizumab (BV) or Cetuximab (Cet) in the first line. A Nanostring platform was used to determine the CMS classification of 392 KRAS wt (codon 12 and 13) primary tumors and correlated it with OS and PFS in patients enrolled in 80405. Methods: CMS for 392 of 431tumors were defined using a custom CRC Nanostring panel (39 CMS classification not possible). Stratified Cox proportional hazard model was used to evaluate the effect of CMS classification stratified by prior radiation, prior chemotherapy, adjusting for age, sex, race, primary in place, liver met only, and sidedness. Results: We found CMS1 (14%), CMS2 (47%), CMS3 (2%), CMS4 (29%), NonConsensus (8%). Results are shown in Table 1. Patients with CMS1 who received BV had significantly longer OS than those who received Cet (HR 0.47, 95% CI [0.24, 0.92]). Patients with CMS2 who received BV tended to have shorter OS than those who received Cet (HR 1.41, CI [0.95, 2.08]). Conclusions: Our data suggest that CMS is associated with OS and PFS in first line therapy in mCRC patients. Preliminary data suggest that certain CMS may be associated with efficacy of Bev and Cet based chemotherapy. CMS classification should be explored as a stratification factor in future trials. Support: U10CA180821, U10CA180830, U10CA180882 Clinical trial information: NCT00265850. [Table: see text]

3504 Background: CALGB 80405 was a randomized phase III trial that found no difference in OS in first-line mCRC pts treated with either bevacizumab (Bev) or cetuximab (Cet). Primary tumor DNA from 361 pts, including KRAS mutant (mut) pts, has been profiled for somatic gene mutations/ML/MSI to discover molecular markers of OS. Methods: Mutations in 11 genes were determined by PCR, MSI by microsatellite analysis, and ML by next-generation sequencing (FoundationOne). Cox proportional hazard models are used, stratified by prior XRT and +/- adjuvant chemotherapy; adjusted by age, race, gender, synchronous vs. metachronous, liver metastases, sidedness, all RAS. Results: BRAF: Mut pts had shorter OS than wild-type (wt) pts (HR 1.92, 95% CI 1.34,2.75; p<0.001); HR 1.65 (1.09,2.50) after adjusting for sidedness (p 0.022). In mut pts longer OS is observed in Bev arm vs. Cet arm (p 0.041); in wt pts no arm difference is observed (p 0.291, table). MSI: OS does not differ between MSI-H and MSI-S pts (HR 0.78 [0.40, 1.52], p 0.450). In MSI-H pts longer OS is observed in Bev arm vs. Cet arm (p 0.002); in MSI-S pts no difference is observed (p 0.305, table). ML: Hypermutated MSI-H pts are excluded. In a subset of 205 pts, pts with ML>5 (N=93) have longer OS than pts with ML≤5 (N=112) (HR 0.65 [0.42,1.00], p 0.048). In Bev arm higher ML confers longer OS than lower ML (HR 0.85 [0.80,0.96], p 0.004); in Cet arm no difference is observed (HR 0.99 [0.90,1.09], p 0.862). Conclusions: BRAF is a strong negative prognostic factor in mCRC, even when sidedness is taken into account. ML is a novel marker for further evaluation. The effect of Bev and Cet in either BRAF mut or MSI-H pts should be tested in larger datasets. Updated results from more screened samples will be presented. [Table: see text]

3503 Background: 80405 found no OS or Progression Free Survival (PFS) difference when bevacizumab (BV) or cetuximab (Cet) was added to 1st-line FOLFOX or FOLFIRI in All RAS wild type (wt) mCRC pts. There was a significant 1° side by biologic interaction (P int: OS = 0.008, PFS = 0.001) favoring pts with left-sided (L) 1°. Analyses of 1° tumors beyond All RAS includes Consensus Molecular Subtype (CMS), BRAF and MSI. (CMS results - see Lenz et al; BRAF -see Innocenti et al) We asked whether 1° tumor location - L vs right (R) - is an independent prognostic marker when these other molecular features are considered. Methods: We used a Cox proportional hazard model stratified by prior XRT and +/- adjuvant chemo; adjusted for age, gender, synchronous vs metachronous, CMS, MSI and BRAF status. Pts with transverse (T) tumors were excluded in this analysis. Results: Sidedness was determined in 782 pts (L - 472; R - 256; T -54). Molecular data from 728 pts (with L - and R-sided 1°s) was available as follows: KRAS -- 291, NRAS -393, BRAF - 393, MSI - 378, CMS - 533. L vs R mOS: 32.9 v 19.6 months (mo) (p < 0.0001). See Table for OS results in All RAS / BRAF wt and BRAF mutant (mut) pts. Sidedness (R vs L) is an independent prognostic marker even after adjusting for all these molecular features: HR = 1.392 (1.032, 1.878), p = 0.031. Conclusions: Primary tumor location is an independent prognostic factor when adjusted for age, gender, synchronous/metachronous, CMS, MSI and BRAF status. We are exploring clinical variables such as tumor burden, metastatic sites and measurability of disease in an attempt to explain the impact of sidedness. Support: U10CA188021, U10CA180882. Eli Lilly and Co, Genentech/Roche, Pfizer, Sanofi. Clinical trial information: NCT002655850. [Table: see text]