Characterization and Clinical Outcomes of DNA Mismatch Repair-deficient Small Bowel Adenocarcinoma

PURPOSE

The prevalence and clinical characteristics of small bowel adenocarcinomas (SBA) in the setting of Lynch syndrome have not been well studied. We characterized SBA according to DNA mismatch repair and/or microsatellite instability (MMR/MSI) and germline mutation status and compared clinical outcomes.

EXPERIMENTAL DESIGN

A single-institution review identified 100 SBAs. Tumors were evaluated for MSI via MSIsensor and/or corresponding MMR protein expression via IHC staining. Germline DNA was analyzed for mutations in known cancer predisposition genes, including MMR (MLH1, MSH2, MSH6, PMS2, and EPCAM). Clinical variables were correlated with MMR/MSI status.

RESULTS

Twenty-six percent (26/100; 95% confidence interval, 18.4-35.4) of SBAs exhibited MMR deficiency (MMR-D). Lynch syndrome prevalence was 10% overall and 38.5% among MMR-D SBAs. Median age at SBA diagnosis was similar in non-Lynch syndrome MMR-D versus MMR-proficient (MMR-P) SBAs (65 vs. 61; P = 0.75), but significantly younger in Lynch syndrome (47.5 vs. 61; P = 0.03). The prevalence of synchronous/metachronous cancers was 9% (6/67) in MMR-P versus 34.6% (9/26) in MMR-D SBA, with 66.7% (6/9) of these in Lynch syndrome (P = 0.0002). In the MMR-P group, 52.2% (35/67) of patients presented with metastatic disease, compared with 23.1% (6/26) in the MMR-D group (P = 0.008). In MMR-P stage I/II patients, 88.2% (15/17) recurred, compared with 18.2% (2/11) in the MMR-D group (P = 0.0002).

CONCLUSIONS

When compared with MMR-P SBA, MMR-D SBA was associated with earlier stage disease and lower recurrence rates, similar to observations in colorectal cancer. With a 38.5% prevalence in MMR-D SBA, germline Lynch syndrome testing in MMR-D SBA is warranted.

Quantitative assessment of tumor-infiltrating lymphocytes in mismatch repair proficient colon cancer

Tumor infiltrating lymphocytes (TIL), which represent host adaptive response to the tumor, were first identified at scanning magnification to select areas with the highest counts on hematoxylin and eosin slides, quantitated per high-power field (HPF), and analyzed for association with recurrence-free survival (RFS) in 848 patients. Highest TIL in a single HPF was analyzed as a continuous and categorical variable, and optimal cutoff analysis was performed to predict RFS. Highest TIL count in a single HPF ranged from 0 to 45, and the optimal cutoff for TIL high vs TIL low was determined to be ≥ 3 vs < 3 with a concordance probability estimate of 0.74. In the entire cohort, 5-year RFS was 90.2% (95% CI = 83.7–94.2) in TIL high compared to 78.9% (95% CI = 74.1–82.9) in TIL low (log rank P < .0001). TIL remained significant in the mismatch repair-proficient (pMMR) cohort where 5-year RFS was 94.6% (95% CI = 88.3–97.5) in TIL high compared to 77.9% (95% CI = 69.2–84.4) in TIL low (P = .008). On multivariable analysis, TIL and AJCC Stage were independently associated with RFS in the pMMR cohort. Qualitatively in the pMMR cohort, RFS in Stage II TIL high patients was similar to that in Stage I patients and RFS in Stage III TIL high was similar to that in Stage II TIL low patients. Assessment of TIL in a single HPF using standard H&E slides provides important prognostic information independent of MMR status and AJCC stage.

Specific Mutations in APC, but Not Alterations in DNA Damage Response, Associate With Outcomes of Patients With Metastatic Colorectal Cancer

In an integrated genomic and clinical analysis, we evaluate the effects of Wnt and DNA damage response pathway alterations on metastatic colorectal cancer.

Discordant DNA mismatch repair protein status between synchronous or metachronous gastrointestinal carcinomas: frequency, patterns, and molecular etiologies

The widespread use of tumor DNA mismatch repair (MMR) protein immunohistochemistry in gastrointestinal tract (GIT) carcinomas has unveiled cases where the MMR protein status differs between synchronous/metachronous tumors from the same patients. This study aims at examining the frequency, patterns and molecular etiologies of such inter-tumoral MMR discordances. We analyzed a cohort of 2159 colorectal cancer (CRC) patients collected over a 5-year period and found that 1.3% of the patients (27/2159) had ≥ 2 primary CRCs, and 25.9% of the patients with ≥ 2 primary CRCs (7/27) exhibited inter-tumoral MMR discordance. We then combined the seven MMR-discordant CRC patients with three additional MMR-discordant GIT carcinoma patients and evaluated their discordant patterns and associated molecular abnormalities. The 10 patients consisted of 3 patients with Lynch syndrome (LS), 1 with polymerase proofreading-associated polyposis (PAPP), 1 with familial adenomatous polyposis (FAP), and 5 deemed to have no cancer disposing hereditary syndromes. Their MMR discordances were associated with the following etiologies: (1) PMS2-LS manifesting PMS2-deficient cancer at an old age when a co-incidental sporadic MMR-proficient cancer also occurred; (2) microsatellite instability-driven secondary somatic MSH6-inactivation occurring in only one-and not all-PMS2-LS associated MMR-deficient carcinomas; (3) "compound LS" with germline mutations in two MMR genes manifesting different tumors with deficiencies in different MMR proteins; (4) PAPP or FAP syndrome-associated MMR-proficient cancer co-occurring metachronously with a somatic MMR-deficient cancer; and (5) non-syndromic patients with sporadic MMR-proficient cancers co-occurring synchronously/metachronously with sporadic MMR-deficient cancers. Our study thus suggests that inter-tumoral MMR discordance is not uncommon among patients with multiple primary GIT carcinomas (25.9% in patients with ≥ 2 CRCs), and may be associated with widely varied molecular etiologies. Awareness of these patterns is essential in ensuring the most effective strategies in both LS detection and treatment decision-making. When selecting patients for immunotherapy, MMR testing should be performed on the tumor or tumors that are being treated.

Correction to: Primary Tumor Location and Outcomes After Cytoreductive Surgery and Intraperitoneal Chemotherapy for Peritoneal Metastases of Colorectal Origin

In the original article there is a reference missing, in addition to its citations in the text. The reference is as follows.

Primary Tumor Location and Outcomes After Cytoreductive Surgery and Intraperitoneal Chemotherapy for Peritoneal Metastases of Colorectal Origin

BACKGROUND

The aim of this study is to evaluate outcomes in patients with peritoneal metastasis of colorectal cancer (pmCRC) who underwent cytoreductive surgery and intraperitoneal chemotherapy (CRS/IPC) in relation to the location of the primary tumor. Regional therapy, including cytoreductive surgery and intraperitoneal chemotherapy, has been associated with improved survival in patients with pmCRC. Location of the primary tumor has been shown to be prognostic in patients with metastasis.

PATIENTS AND METHODS

A retrospective review was performed for all patients who underwent complete cytoreduction and intraperitoneal chemotherapy from 2010 to 2017, examining patient and tumor characteristics, overall and recurrence-free survival, recurrence patterns, and tumor mutational profiles.

RESULTS

Ninety-three patients were included in the study: 49 (53%) with a right-sided and 44 (47%) with a left-sided primary tumor. Patients with a right-sided tumor had significantly shorter recurrence-free survival (median, 6.3 months; 95% CI, 4.7-8.1 months vs 12.3 months; 95% CI, 3.6-21.7 months; P = 0.02) and overall survival (median, 36.6 months; 95% CI, 26.4-46.9 months vs 83.3 months; 95% CI 44.2-122.4 months; P = 0.03). BRAF and KRAS mutations were more frequent in right-sided tumors, and APC and TP53 mutations were more frequent in left-sided tumors, which were more chromosomally instable. BRAF mutations were associated with early recurrence.

CONCLUSIONS

Tumor sidedness is a predictor of oncological outcomes after CRS/IPC. Tumor sidedness and molecular characteristics should be considered when counseling patients regarding expected outcomes and when selecting or stratifying pmCRC patients for clinical trials of regional therapy.

EGFR Blockade Reverts Resistance to KRASG12C Inhibition in Colorectal Cancer

Most patients with KRAS G12C-mutant non-small cell lung cancer (NSCLC) experience clinical benefit from selective KRASG12C inhibition, whereas patients with colorectal cancer bearing the same mutation rarely respond. To investigate the cause of the limited efficacy of KRASG12C inhibitors in colorectal cancer, we examined the effects of AMG510 in KRAS G12C colorectal cancer cell lines. Unlike NSCLC cell lines, KRAS G12C colorectal cancer models have high basal receptor tyrosine kinase (RTK) activation and are responsive to growth factor stimulation. In colorectal cancer lines, KRASG12C inhibition induces higher phospho-ERK rebound than in NSCLC cells. Although upstream activation of several RTKs interferes with KRASG12C blockade, we identify EGFR signaling as the dominant mechanism of colorectal cancer resistance to KRASG12C inhibitors. The combinatorial targeting of EGFR and KRASG12C is highly effective in colorectal cancer cells and patient-derived organoids and xenografts, suggesting a novel therapeutic strategy to treat patients with KRAS G12C colorectal cancer. SIGNIFICANCE: The efficacy of KRASG12C inhibitors in NSCLC and colorectal cancer is lineage-specific. RTK dependency and signaling rebound kinetics are responsible for sensitivity or resistance to KRASG12C inhibition in colorectal cancer. EGFR and KRASG12C should be concomitantly inhibited to overcome resistance to KRASG12C blockade in colorectal tumors.See related commentary by Koleilat and Kwong, p. 1094.This article is highlighted in the In This Issue feature, p. 1079.

Lineage Reversion Drives WNT Independence in Intestinal Cancer

The WNT pathway is a fundamental regulator of intestinal homeostasis, and hyperactivation of WNT signaling is the major oncogenic driver in colorectal cancer. To date, there are no described mechanisms that bypass WNT dependence in intestinal tumors. Here, we show that although WNT suppression blocks tumor growth in most organoid and in vivo colorectal cancer models, the accumulation of colorectal cancer-associated genetic alterations enables drug resistance and WNT-independent growth. In intestinal epithelial cells harboring mutations in KRAS or BRAF, together with disruption of TP53 and SMAD4, transient TGFβ exposure drives YAP/TAZ-dependent transcriptional reprogramming and lineage reversion. Acquisition of embryonic intestinal identity is accompanied by a permanent loss of adult intestinal lineages, and long-term WNT-independent growth. This work identifies genetic and microenvironmental factors that drive WNT inhibitor resistance, defines a new mechanism for WNT-independent colorectal cancer growth, and reveals how integration of associated genetic alterations and extracellular signals can overcome lineage-dependent oncogenic programs. SIGNIFICANCE: Colorectal and intestinal cancers are driven by mutations in the WNT pathway, and drugs aimed at suppressing WNT signaling are in active clinical development. Our study identifies a mechanism of acquired resistance to WNT inhibition and highlights a potential strategy to target those drug-resistant cells.This article is highlighted in the In This Issue feature, p. 1426.

BRAF-Mutant Transcriptional Subtypes Predict Outcome of Combined BRAF, MEK, and EGFR Blockade with Dabrafenib, Trametinib, and Panitumumab in Patients with Colorectal Cancer

PURPOSE

The influence of the transcriptional and immunologic context of mutations on therapeutic outcomes with targeted therapy in cancer has not been well defined. BRAF V600E-mutant (BM) colorectal cancer comprises two main transcriptional subtypes, BM1 and BM2. We sought to determine the impact of BM subtype, as well as distinct biological features of those subtypes, on response to BRAF/MEK/EGFR inhibition in patients with colorectal cancer.

PATIENTS AND METHODS

Paired fresh tumor biopsies were acquired at baseline and on day 15 of treatment from all consenting patients with BM colorectal cancer enrolled in a phase II clinical trial of dabrafenib, trametinib, and panitumumab. For each sample, BM subtype, cell cycle, and immune gene signature expression were determined using RNA-sequencing (RNA-seq), and a Cox proportional hazards model was applied to determine association with progression-free survival (PFS).

RESULTS

Confirmed response rates, median PFS, and median overall survival (OS) were higher in BM1 subtype patients compared with BM2 subtype patients. Evaluation of immune contexture identified greater immune reactivity in BM1, whereas cell-cycle signatures were more highly expressed in BM2. A multivariate model of PFS incorporating BM subtype plus immune and cell-cycle signatures revealed that BM subtype encompasses the majority of the effect.

CONCLUSIONS

BM subtype is significantly associated with the outcome of combination dabrafenib, trametinib, and panitumumab therapy and may serve as a standalone predictive biomarker beyond mutational status. Our findings support a more nuanced approach to targeted therapeutic decisions that incorporates assessment of transcriptional context.

Encorafenib plus cetuximab with or without binimetinib for BRAF V600E-mutant metastatic colorectal cancer: Quality-of-life results from a randomized, three-arm, phase III study versus the choice of either irinotecan or FOLFIRI plus cetuximab (BEACON CRC)

4039

Background: In the BEACON CRC study, the triplet regimen of encorafenib (ENCO) + binimetinib (BINI) + cetuximab (CETUX) significantly improved overall survival (OS, HR:0.52, P < 0.0001) and objective response rates (ORR, 26% vs 2%, P < 0.0001) in patients (pts) with BRAFV600E metastatic colorectal cancer (mCRC) compared with current standard of care. This analysis focuses on the patient-reported quality of life (QOL) assessments from this study. Methods: The BEACON CRC study was a randomized, open-label, 3-arm, phase 3 global study which evaluated triplet (ENCO+BINI+CETUX) or doublet (ENCO+CETUX) vs. investigator’s choice of irinotecan + CETUX or FOLFIRI + CETUX in pts with BRAFV600E mCRC. QOL assessments (secondary endpoints in the trial) included the EORTC QOL Questionnaire (QLQ C30), Functional Assessment of Cancer Therapy Colon Cancer (FACT C), EuroQol 5D 5L, and Patient Global Impression of Change (PGIC). The primary assessment for the QOL variables was the time to definitive 10% deterioration. The study is ongoing. Results: 665 pts were randomly assigned to receive either triplet (n = 224), doublet (n = 220), or control (n = 221). Reduction in the risk of QOL deterioration was an estimated 45% (HR 0.55, 95% CI: 0.43, 0.70) and 52% (HR 0., 9485% CI: 0.38, 0.62) in EORTC QLQ C30 and FACT C assessments, respectively, in favor of the triplet regimen over control. For the doublet vs. control, reduction in risk of QOL deterioration was an estimated 46% (HR 0.54, 95% CI: 0.43, 0.69) and 54% (HR 0.46, 95% CI: 0.36, 0.59) in EORTC QLQ C30 and FACT C, respectively in favor of the doublet. Similar results were observed in EuroQol 5D 5L and PGIC assessments. There were no overall differences in QOL between triplet and doublet across the 4 instruments. Conclusions: In BEACON CRC, triplet and doublet demonstrated substantial improvement in patient-reported QOL assessments over the current standard of care in pts with BRAFV600E-mutant metastatic CRC whose disease had progressed after 1 or 2 prior regimens. Clinical trial information: NCT02928224 .

Do differences in the microbiome explain early onset in colon cancer?

e16070

Background: Intestinal dysbiosis has been hypothesized as a possible etiology of the increasing incidence of early-onset colon cancer (EO-CC). Here, we compare the microbiome signature in nonmetastatic, microsatellite stable (MSS) EO-CC to average-onset colon cancer (AO-CC). Methods: Specimens from patients with resected stage I-III MSS colon cancer from 2014-2019 were sequenced by MSK-IMPACT, a large panel next generation sequencing (NGS) assay. A validated technique using non-human read sequences from NGS analysis was used to identify the microbial species in tumor tissue. The tumor microbial alpha diversity and differentially abundant microbiome were compared between patients younger than 40 years (EO-CC) with those older than 60 years (AO-CC). Results: Of 275 patients with MSS, 24 (mean 33.6, range 24-39) and 114 patients (mean 70, range 61-90) had EO-CC and AO-CC, respectively. There was no significant difference in clinicopathological features including gender, tumor stage and neoadjuvant treatment between the two groups. EO-CC was more likely to present with left sided disease compared to AO-CC (81% vs. 45%, p = 0.001). There was no significant difference in the tumor microbial diversity (alpha diversity) between the EO-CC and AO-CC (pShannon= 0.95). Although there was a relative abundance of microbial species from bacterial phylum such as Actinobacteria, Deinococcus-Thermus, α-proteobacteria, γ-proteobacteria and δ-proteobacteria in EO-CC compared to AO-CC, this difference was not significant after controlling for multiple comparisons (Table). Conclusions: Our analysis did not reveal a significant difference between EO-CC and AO-CC in both the abundance and diversity of tumor microbial species, suggesting intestinal dysbiosis may not be a major driver in early onset colorectal cancer pathogenesis. However, additional studies with a larger sample size are warranted for further analysis and subgroup comparison. [Table: see text]

Encorafenib plus cetuximab with or without binimetinib for BRAF V600E metastatic colorectal cancer: Updated survival results from a randomized, three-arm, phase III study versus choice of either irinotecan or FOLFIRI plus cetuximab (BEACON CRC)

4001

Background: BEACON CRC is a randomized, phase 3 study which evaluated the triplet of encorafenib (ENCO) + binimetinib (BINI) + cetuximab (CETUX) and the doublet of ENCO + CETUX vs. investigator’s choice of irinotecan + CETUX or FOLFIRI + CETUX in patients (pts) with BRAFV600E metastatic colorectal cancer (mCRC) whose disease had progressed after 1-2 prior regimens in the metastatic setting. Primary endpoints were overall survival (OS) and objective response rate (ORR; by blinded central review) for triplet vs control. In a previous interim analysis, triplet and doublet improved OS and ORR versus standard of care. Here we report on an updated analysis. Methods: Updated analysis includes 6 months of additional follow-up and response data for all randomized pts. The study is ongoing. Results: Pts received triplet (n=224), doublet (n=220), or control (n=221). Median OS was 9.3 months (95% confidence interval [CI]:8.2, 10.8) for triplet and 5.9 months (95% CI:5.1-7.1) for control (hazard ratio [HR] (95% CI): 0.60 (0.47-0.75)). Median OS for doublet was 9.3 months (95% CI: 8.0-11.3) (HR vs. control: 0.61 (0.48-0.77). Confirmed ORR was 26.8% (95% CI: 21.1%-33.1%) for triplet, 19.5% (95% CI: 14.5%-25.4%) for doublet, and 1.8% (95% CI: 0.5%-4.6%) for control. Retrospective subgroup analyses suggested some pts may benefit more from triplet than doublet therapy (Table). Both triplet and doublet showed improved OS compared to control in all subgroups. Adverse events were consistent with prior analysis, with grade ≥3 adverse events in 65.8%, 57.4%, and 64.2% for triplet, doublet and control, respectively. Conclusions: The updated analysis of the BEACON CRC study confirmed that encorafenib + cetuximab with or without binimetinib improved OS and ORR in previously treated pts with BRAF V600E mCRC compared with standard chemotherapy. Clinical trial information: NCT02928224 . [Table: see text]

A phase II study of induction PD-1 blockade in subjects with locally advanced mismatch repair-deficient rectal adenocarcinoma

TPS4123

Background: The treatment of patients with locally advanced rectal cancer includes total neoadjuvant therapy with chemotherapy, chemoradiation followed by surgery. While most rectal cancers respond to combination induction chemotherapy, patients with mismatch repair deficient (dMMR) or MSI-H tumors have a significantly higher chance of progression with this treatment regimen. dMMR or MSI-H tumors have shown remarkable responses to PD-1 blockade, but the effect of neoadjuvant checkpoint inhibition has not been well studied. In this trial we will determine the pathologic complete response rate (pCR) of neoadjuvant anti-PD-1 blockade followed by standard chemoradiation in dMMR or MSI-H locally advanced rectal cancer. We hypothesize that treatment naïve dMMR or MSI-H rectal cancers will achieve a robust clinical response to PD-1 blockade and that the total neodjuvant therapy with PD-1 blockade followed by chemoradiation will improve pCR rates. Methods: Eligible patients ≥18 years of age with Stage II (T3-4, N-) or Stage III (any T, N+) histologically confirmed dMMR or MSI-H (by NGS) rectal adenocarcinoma will be enrolled. Patients will receive TSR-042 (500mg IV) every 3 weeks for a maximum of 8 cycles (6 months of treatment). Imaging, internal endoscopic exam and ctDNA blood draw will be performed at 6 weeks and every 3 months during induction anti-PD-1 treatment. Adverse events and surgical complications will be graded according to the NCI CTCAE v5 and the Clavien-Dindo classification, respectively. Following neoadjuvant checkpoint blockade, patients will undergo conventional chemoradiotherapy followed by surgical resection. The primary endpoint is pathologic complete response compared with historical control in pMMR patients. Patients will be followed up every 6 months for assessment of disease-free survival for up to five years. Clinical trial information: NCT04165772 .

Actionable alterations (AA) in gastrointestinal (GI) cancers: Rate of detection and receipt of matched therapies (MT)

e15677

Background: Next generation sequencing (NGS) is widely used in pts with advanced cancer to personalize care. Current NCCN guidelines endorse Her2, PD-L1 and MSI testing in esophagogastric cancer (EGC), RAS, BRAF, Her2 and MSI testing in colorectal cancer (CRC) and germline, somatic and MSI testing in pancreas cancer (PC). The proportion of GI cancer pts who receive MT based on NGS is unclear. Methods: We identified pts with advanced EGC (2016-18), PC (2017) and CRC (2016) who underwent NGS with MSK-IMPACT. We assessed the proportion of pts with ≥1 AA as defined by OncoKB (at the time of analysis, levels 1/2a were accepted practice and levels 2b/3/4 were investigational; Chakravaty, JCO PO 2017), those who received MT on trial or off label and 3 and 6 months (mos) progression-free survival (PFS). Results: We identified 260 EGC, 357 PC and 438 CRC pts. After excluding pts who had ongoing benefit from standard therapy (tx), were treated elsewhere or had no active stage IV disease, potential level 2/3/4 AAs occurred in 37% (n = 97) of EGC pts, 32.5% (n = 116) of PC pts and 26.7% (n = 117) of CRC pts (Table). 10, 1 and 17 pts with EGC, PC and CRC respectively were MSI. 1 pt in each subtype had an NTRK fusion (OncoKB level 1). In EGC, 6 pts (6.2% of those with AAs) received MT: 2 pts with MET amplification (a) and 1 each with BRCA2 mutation (m), TSC2m, ERBB2m and EGFRa. The pts with METa treated with crizotinib achieved 3 but not 6 mos PFS. In PC, 11 pts (9.5%) got MT: 10 pts for BRCAm and 1 for NTRK3 fusion. 9 pts with BRCAm treated with PARP inhibitors (i) achieved ≥3 mos PFS and 5 pts reached ≥6 mos PFS. The pt treated with NTRKi progressed rapidly. In CRC, 5 pts with ERBB2a and 9 pts with BRAFm received MT (12%). 3 pts and 2 pts treated with anti-Her2 tx achieved ≥3 and ≥6 mos PFS respectively. Of 6 pts treated with BRAF/MEKi plus irinotecan or anti-EGFR tx, all achieved ≥3 mos PFS; 3 reached ≥6 mos PFS. 3 pts received novel BRAF and ERK1/2i; none reached 3 mos PFS. Conclusions: NGS frequently identified OncoKB level 2 AAs. Few pts received MT, and of those, some achieved ≥6 mos PFS. Pts with CRC and PC received MT which subsequently became standard NCCN recommendations; therefore, a more current analysis may show increased MT use. Still, MT for level 3 and 4 alterations were rare, suggesting expectations of NGS must be managed appropriately. [Table: see text]

Mismatch Repair-Deficient Rectal Cancer and Resistance to Neoadjuvant Chemotherapy

PURPOSE

Evaluate response of mismatch repair-deficient (dMMR) rectal cancer to neoadjuvant chemotherapy.

EXPERIMENTAL DESIGN

dMMR rectal tumors at Memorial Sloan Kettering Cancer Center (New York, NY) were retrospectively reviewed for characteristics, treatment, and outcomes. Fifty patients with dMMR rectal cancer were identified by IHC and/or microsatellite instability analysis, with initial treatment response compared with a matched MMR-proficient (pMMR) rectal cancer cohort. Germline and somatic mutation analyses were evaluated. Patient-derived dMMR rectal tumoroids were assessed for chemotherapy sensitivity.

RESULTS

Of 21 patients receiving neoadjuvant chemotherapy (fluorouracil/oxaliplatin), six (29%) had progression of disease. In comparison, no progression was noted in 63 pMMR rectal tumors (P = 0.0001). Rectal cancer dMMR tumoroids reflected this resistance to chemotherapy. No genomic predictors of chemotherapy response were identified. Of 16 patients receiving chemoradiation, 13 (93%) experienced tumor downstaging; one patient had stable disease, comparable with 48 pMMR rectal cancers. Of 13 patients undergoing surgery, 12 (92%) had early-stage disease. Forty-two (84%) of the 50 patients tested positive for Lynch syndrome with enrichment of germline MSH2 and MSH6 mutations when compared with 193 patients with Lynch syndrome-associated colon cancer (MSH2, 57% vs 36%; MSH6, 17% vs 9%; P < 0.003).

CONCLUSIONS

Over one-fourth of dMMR rectal tumors treated with neoadjuvant chemotherapy exhibited disease progression. Conversely, dMMR rectal tumors were sensitive to chemoradiation. MMR status should be performed upfront in all locally advanced rectal tumors with careful monitoring for response on neoadjuvant chemotherapy and genetic testing for Lynch syndrome in patients with dMMR rectal cancer.

Systemic Chemotherapy for Metastatic Colitis-Associated Cancer Has a Worse Outcome Than Sporadic Colorectal Cancer: Matched Case Cohort Analysis

BACKGROUND

Colitis-associated cancers (CAC) are a catastrophic complication of inflammatory bowel disease; at diagnosis, CAC is frequently at an advanced stage. Although the genomic alterations (GA) in CAC are different from sporadic colorectal cancer (CRC), the same systemic therapies are used. We compared clinically relevant outcomes using standard care systemic chemotherapy of stage IV CAC versus a matched patient control cohort of stage IV CRC patients.

PATIENTS AND METHODS

A retrospective matched cohort design was used. Eighteen cases of stage IV CAC (7 ulcerative colitis, 11 Crohn disease) and 18 CRC were identified. GA analysis was available for all patients. Outcome endpoints included response rate and response duration, progression-free survival, and OS.

RESULTS

Although the response rates were similar (CAC 35.7% vs. CRC 57.1%, P = .45), the median duration of response for CAC was significantly shorter (1.4 months, vs. CRC 11.8 months, P = .006). There was no difference in dose density of first-line therapy between cohorts, suggesting that shorter response duration was due to more rapid development of chemotherapy resistance. Median OS was significantly shorter for CAC patients (13 vs. 27.6 months, P = .034). As expected, there was a difference in the spectrum of GA between CAC and CRC cohorts. However, GA associated with poor prognosis (eg, B-Raf) were no more frequent in the CAC cohort.

CONCLUSION

Clinically meaningful outcomes of duration of response and OS are worse for CAC versus sporadic CRC patients treated with FOLFOX or FOLFIRI as first therapy for metastatic disease.

Genomic alterations in colitis-associated cancers in comparison to those found in sporadic colorectal cancer and present in precancerous dysplasia

191

Background: Patients with inflammatory bowel disease (IBD) [Crohn’s disease (CD) and ulcerative colitis (UC)] are at increased risk for small bowel or colorectal cancers (Colitis Associated Cancers, CAC). Currently CAC is treated the same as sporadic colorectal cancer (CRC) with significantly shorter overall survival for advanced CAC compared to matched patients with CRC. In a pilot series, we found that tumors developing in IBD have distinct genomic alterations (GA) with potential implications for early detection and treatment. We now extend this analysis and characterize the relationship of GA in synchronous dysplasia and cancer. Methods: 104 CAC (54 UC-associated and 50 CD-associated) were sequenced with targeted-exome sequencing of > 300 cancer-related genes. GA in CAC were compared to those reported for sporadic CRC. Whole exome sequencing was performed on paired mucosa, dysplasia and carcinoma samples obtained from 15 colectomy specimens; in these cases, expert pathology review confirmed normal appearing mucosa intervening between areas of dysplasia and CAC. Results: TP53 mutations (89%), MYC amplifications (24%), and cell cycle copy number alterations (20%) were significantly enriched in CAC compared to sporadic CRC, while APC alterations (21%) were significantly less common in CAC compared to sporadic CRC. Distinct GA in CAC consisted of IDH1 R132 mutations (7%) and FGFR pathway alterations (7%). While IDH1 R132 mutations and PI3K pathway alterations were more common in CD-associated CAC, MAPK ( BRAF/ MEK1) alterations were more common in UC-associated CAC. GA in CACs did not significantly vary by duration of preceding IBD. GA were often shared in dysplasia and carcinoma, despite normal-appearing intervening mucosa. GA involving TP53, APC, KRAS, and IDH1 mutations were identified in dysplasia and shared between CAC and dysplasia. Conclusions: CAC exhibit distinct GA compared to sporadic CRC with near universal TP53 mutation, increased copy number alterations involving transcription factors and cell cycle genes, and unique drivers. A field effect can be seen for GA between distant dysplasia and carcinoma, but many GA remain private to CAC.

Encorafenib plus cetuximab with or without binimetinib for BRAF V600E-mutant metastatic colorectal cancer: Quality-of-life results from a randomized, three-arm, phase III study versus the choice of either irinotecan or FOLFIRI plus cetuximab (BEACON CRC)

8

Background: In the BEACON CRC study, the triplet regimen of encorafenib (ENCO) + binimetinib (BINI) + cetuximab (CETUX) significantly improved overall survival (OS, HR:0.52, P < 0.0001) and objective response rates (ORR, 26% vs 2%, P < 0.0001) in patients (pts) with BRAF V600E metastatic colorectal cancer (mCRC) compared with current standard of care. This analysis focuses on the patient-reported quality of life (QOL) assessments from this study. Methods: The BEACON CRC study was a randomized, open-label, 3-arm, phase 3 global study which evaluated triplet (ENCO+BINI+CETUX) or doublet (ENCO+CETUX) vs. investigator’s choice of irinotecan + CETUX or FOLFIRI + CETUX in pts with BRAFV600E mCRC. QOL assessments (secondary endpoints in the trial) included the EORTC QOL Questionnaire (QLQ C30), Functional Assessment of Cancer Therapy Colon Cancer (FACT C), EuroQol 5D 5L, and Patient Global Impression of Change (PGIC). The primary assessment for the QOL variables was the time to definitive 10% deterioration between arms. Results: 665 pts were randomly assigned to receive either triplet (n = 224), doublet (n = 220), or control (n = 221). Reduction in the risk of QOL deterioration was an estimated 45% (HR 0.55, 95% CI: 0.43, 0.70) and 44% (HR 0.56, 95% CI: 0.44, 0.71) in EORTC QLQ C30 and FACT C assessments, respectively, in favor of the triplet regimen over control. For the doublet vs. control, reduction in risk of QOL deterioration was an estimated 46% (HR 0.54, 95% CI: 0.43, 0.69) and 43% (HR 0.57, 95% CI: 0.45, 0.72) in EORTC QLQ C30 and FACT C, respectively in favor of the doublet. Similar results were observed in EuroQol 5D 5L and PGIC assessments. There were no overall differences in QOL between triplet and doublet across the 4 instruments. Conclusions: In BEACON CRC, triplet and doublet demonstrated substantial improvement in patient-reported QOL assessments over the current standard of care in pts with BRAF V600E-mutant metastatic CRC whose disease had progressed after 1 or 2 prior regimens. Clinical trial information: NCT02928224.

Genomic characterization of rectal cancer and molecular determinants of response to neoadjuvant chemoradiotherapy

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Background: Rectal cancers are clinically different from colon cancers and have not yet been molecularly characterized due to the scarcity of pretreatment specimens. Discovery of molecular determinants of response to chemotherapy and radiation in patients with locally advanced rectal cancer (LARC, stage II and III) are needed to select those who can avoid surgery and benefit from watch-and-wait strategies. Methods: We profiled 371 pre-treatment specimens using targeted-exome sequencing of 468 cancer genes (n = 325), whole-exome sequencing (n = 100), and RNA-sequencing (n = 113). The targeted-sequencing cohort included patients with stage I (n = 44), II (n = 41), III (n = 176), and IV (n = 64) disease. Primary tumors were divided into lower (LR: 0-4 cm to anal verge, n = 62), middle (MR: 4-8 cm, n = 115), and upper rectum (UR: 8-12 cm, n = 107). We examined molecular determinants of complete response (CR) and relapse free survival (RFS) in LARC patients treated with chemoradiotherapy only (CRT: n = 39), induction chemotherapy + CRT (INCT: n = 87) and consolidation chemotherapy after CRT (CCNT: n = 63). Results: Among MSS cases, oncogenic gene and signaling pathway alterations did not vary by clinical stage. WNT pathway alterations, driven by APC mutations, were more frequent in the UR (89% UR v 86% MR v 60% LR, p < 0.001) while RTK/RAS alterations were more frequent in the LR (54% UR v 69% MR v 72% LR, p < 0.03). A set of genes enriched in mTOR signaling, G2M checkpoint, EMT transition, and DNA repair were overexpressed in the UR (FDR < 0.1). The 5-yr RFS rate for LARC was 75% (CI: 68%-82%) and 24% of the cases had a CR (n = 45). MSI cases had a higher rate of CR compared to MSS cases (50% v 23%, p = 0.07) and none relapsed (n = 8). KRAS-altered MSS tumors exhibited worse RFS in cases treated with CNCT (5-yr: 74% v 97%, p = 0.01), but not in cases treated with INCT (5-yr: 67% v 72%, p = 0.7). Conclusions: WNT alterations are more frequent in the UR while RTK/RAS alterations are more frequent in the LR, suggesting differences in tumor biology between proximal and distal rectal cancer. Further, we report correlations between distinct molecular profiles and response to treatment paradigms that could guide the design of future clinical trials.

Overcoming Adaptive Resistance to KRAS Inhibitors Through Vertical Pathway Targeting

KRAS G12C inhibitors have shown promise in KRAS G12C-mutant lung cancer but intrinsic and acquired resistance are common. Cotreatment with inhibitors of the protein phosphatase SHP2 can abrogate the adaptive response of cancer cells to KRAS inhibitors resulting in greater suppression of MAPK signaling and enhanced tumor growth inhibition.See related article by Ryan et al., p. 1633.