Tougeron, David

Background Tumors with mismatch repair deficiency (MMRd) classically display concomitant loss of MLH1/PMS2 or MSH2/MSH6 on immunohistochemistry (IHC) with microsatellite instability-high (MSI-High) status on molecular testing. Nevertheless, a different phenotype can occur in up to 15% of MMRd tumors (unusual phenotype). Data on the efficacy of immunotherapy in this population remain scarce. Methods We conducted a retrospective study within the IMMUNODIG MSI cohort including patients with advanced gastrointestinal MMRd tumors treated with immune checkpoint blockade in the real-world setting. We selected patients with both IHC and MSI assays data available. Unusual MMRd tumors were classified into four distinct groups: (1) isolated loss of PMS2 or MSH6 with MSI-H (isolated/MSI-H), (2) complex loss of MMR proteins with MSI-H (complex/MSI-H), (3) loss of one or more MMR proteins without MSI-H (MMRd-IHC/microsatellite stability (MSS) or MSI-low (MSI-L)), and (4) four MMR proteins retained with MSI-H (retained IHC/MSI-H). Results Out of 759 patients in the IMMUNODIG-MSI cohort, 571 patients met inclusion criteria. Of these, 90 (15.8%) had an unusual phenotype (47 isolated/MSI-H, 19 complex/MSI-H, 16 MMRd-IHC/MSS or MSI-L and 8 retained IHC/MSI-H). Compared with classical phenotypes, patients with a tumor harboring an unusual phenotype had a younger age at treatment (p=0.005), increased RAS mutation (p=0.005), reduced BRAF p.V600E mutation rates (p<0.001), a higher proportion of Lynch syndrome (p<0.001) and a higher prevalence of non-colorectal cancers (p=0.021). After a median follow-up of 28.1 months (mo), there was a significant difference in progression-free survival, with median values of not reached, 66.4 mo, 37.2 mo, 18.3 mo and 5.5 mo for complex/MSI-H, isolated/MSI-H, classical, retained IHC/MSI-H and MMRd-IHC/MSS or MSI-L subgroups, respectively (p<0.001). Notably, objective response rates were 59.1%, 58.7%, and 63.2% for complex/MSI-H, isolated/MSI-H and classical contrasting with 50% and 25% for retained IHC/MSI-H and MMRd-IHC/MSS or MSI-L, with no complete response observed in the latter two. Conclusion Our findings underscore the need for dual testing and advocate for the presence of both MMRd-IHC and MSI-H for optimal immunotherapy response. Of note, complex MMR aberrations and isolated PMS2/MSH6 losses with MSI-H may represent promising candidates for enhanced immunotherapy efficacy.

Background Immune checkpoint inhibitors (ICIs) are recommended to treat patients with deficient mismatch repair/microsatellite instability high (dMMR/MSI-H) metastatic colorectal cancer (mCRC). Pivotal trials have fixed a maximum ICI duration of 2 years, without a compelling rationale. A shorter treatment duration has the potential to improve patients' quality of life and reduce both toxicity and cost without compromising efficacy. Here we examine whether early treatment discontinuation (ETD) before 13 months in patients without progressive disease (PD) can lead to similar long-term disease control compared with a longer treatment duration (LTD). Methods To assess whether ETD is associated with similar outcomes compared with LTD, we assembled an international cohort of patients with dMMR/MSI-H mCRC treated with ICIs who stopped treatment for a reason other than PD within 395 days (ETD group) and compared them to those who continued for >395 days (LTD group). Outcomes were adjusted for patient/tumor characteristics. Primary endpoint was progression-free survival (PFS) and secondary endpoints were objective response rate (ORR), overall survival (OS) and safety. Results Of 976 patients, 137 and 394 were allocated to the ETD and LTD groups, respectively. In the ETD group, treatment was discontinued due to toxicity (n=56), objective response (n=43), surgery (n=28), patient decision (n=2) or other reasons (n=8). Baseline characteristics were well balanced between the two groups: 22% in both groups received both anti-programmed death-(ligand) 1 (anti-PD-(L)1) + anti-cytotoxic T-lymphocyte antigen-4 (anti-CTLA-4); all others received anti-PD-(L)1 monotherapy. ORR to ICIs was 81% in both groups. Median duration of treatment was ~7 months in the ETD and ~24 months in the LTD group. After a median follow-up of 44 months (IQR: 30–67), similar PFS (HR: 0.92, 95% CI: 0.60 to 1.40, p=0.69) and OS (HR: 1.15, 95% CI: 0.66 to 1.99, p=0.62) from the start of ICIs were observed in ETD and LTD patients. In the ETD group, 28 (20%) patients had a PFS event and 9 restarted ICIs with a disease control rate of 66%. Conclusions In our international series of dMMR/MSI-H mCRC, ETD of ICIs in the absence of PD did not seem detrimental in terms of PFS and OS compared with continuing treatment beyond 1 year. Randomized clinical trials to compare short and long treatment duration are now warranted.

Abstract Purpose: We examined the prognostic impact of specific KRAS mutations in patients with stage III colon adenocarcinoma receiving adjuvant FOLFOX alone or combined with cetuximab in a phase III trial (N0147). Analysis was restricted to BRAF–wild-type tumors, because BRAF mutation was associated with poor prognosis, and BRAF and KRAS mutations are mutually exclusive. Experimental Design: The seven most common KRAS mutations in codon 12 and codon 13 were examined in 2,478 BRAF–wild-type tumors. Because KRAS mutations in codon 12 (n = 779) or 13 (n = 220) were not predictive of adjuvant cetuximab benefit, study arms were pooled for analysis. Disease-free survival (DFS) was evaluated by HRs using Cox models. Results: KRAS mutations in codon 12 (multivariate HR, 1.52; 95% confidence interval, CI, 1.28–1.80; P &lt; 0.0001) or codon 13 (multivariate HR, 1.36; 95% CI, 1.04–1.77; P = 0.0248) were significantly associated with shorter DFS compared with patients with wild-type KRAS/BRAF tumors, independent of covariates. KRAS codon 12 mutations were independently associated with proficient mismatch repair (P &lt; 0.0001), proximal tumor site (P &lt; 0.0001), low grade, age, and sex, whereas codon 13 mutations were associated with proximal site (P &lt; 0.0001). Conclusion: KRAS mutations in either codon 12 or 13 are associated with inferior survival in patients with resected stage III colon cancer. These data highlight the importance of accurate molecular characterization and the significant role of KRAS mutations in both codons in the progression of this malignancy in the adjuvant setting. Clin Cancer Res; 20(11); 3033–43. ©2014 AACR.

Abstract Abundant epidemiologic evidence indicates that regular and long-term use of aspirin is associated with a significant reduction in the incidence of colorectal cancer. The long duration of aspirin needed to prevent colorectal cancer is believed to be due to inhibition of precursor lesions known as adenomas, the recurrence of which is inhibited by aspirin in randomized trials. Aspirin intake has also been associated with a statistically significant improvement in patient survival after curative resection of colorectal cancer in large observational studies. In these cohorts, the survival benefit of aspirin was shown to depend upon the level of COX-2 expression in the primary colorectal cancer. More recent analysis of patient tumors from these observational cohorts suggests that the benefit of aspirin may be limited to specific molecular subtypes. Aspirin intake following colorectal cancer resection was associated with a significant improvement of survival in patients whose tumors carried mutant, but not wild-type, copies of the phosphoinositide 3-kinase (PI3KCA) gene, especially tumors that overexpressed COX-2. A mechanistic explanation is suggested by the finding that inhibition of COX-mediated prostaglandin E2 synthesis by aspirin attenuates PI3K signaling activity that is known to regulate cancer cell proliferation and survival. Aspirin has also been shown to reduce the incidence of colorectal cancers bearing wild-type, but not mutant alleles of the BRAFV600E oncogene. Although provocative, the potential utility of these molecular markers for predicting aspirin efficacy awaits prospective evaluation in clinical trials. If validated, these findings may support a personalized approach to using aspirin for the therapy of colorectal cancer. Clin Cancer Res; 20(5); 1087–94. ©2013 AACR.

BACKGROUNDA point mutation (V600E) in the BRAF oncogene is a prognostic biomarker and may predict for nonresponse to anti‐EGFR antibody therapy in patients with colorectal carcinoma. BRAFV600E mutations are frequently detected in tumors with microsatellite instability and indicate a sporadic origin. We used a mutation‐specific antibody to examine mutant BRAFV600E protein expression and its concordance with BRAFV600E mutation data.METHODSPrimary stage III colon carcinomas were analyzed for BRAFV600E mutations in exon 15, and 50 BRAFV600E mutation carriers and 25 wild‐type tumors were selected for analysis of BRAF proteins by immunohistochemistry (IHC). IHC was performed in archival tissue specimens using a pan‐BRAF antibody and a mutation‐specific antibody against BRAFV600E proteins. Staining was scored by 2 pathologists who were blinded to clinical and mutation data.RESULTSUsing a pan‐BRAF antibody, total BRAF protein expression was observed in the tumor cell cytoplasm in 74 of 75 colon carcinomas. A mutation‐specific antibody identified diffuse cytoplasmic staining of mutant BRAFV600E proteins in 49 of 74 cancers. Analysis using a polymerase chain reaction‐based assay revealed that all 49 of these cancers carried BRAFV600E mutations. In contrast, BRAFV600E staining was absent in all 25 tumors that carried wild‐type copies of BRAF.CONCLUSIONSA BRAF mutation‐specific (V600E) antibody detected tumors with BRAFV600E mutations and exhibited complete concordance with a DNA‐based method. These results support the use of IHC as a simplified strategy to screen colorectal cancers for BRAFV600E mutations in clinical practice. Cancer 2013;119:2765–2770. © 2013 American Cancer Society.