Prevalence and Clinical Implications of Mismatch Repair-Proficient Colorectal Cancer in Patients With Lynch Syndrome

PURPOSE

Lynch syndrome (LS)-associated colorectal cancer (CRC) is characterized by mismatch repair-deficiency (MMR-D) and/or microsatellite instability (MSI). However, with increasing utilization of germline testing, MMR-proficient (MMR-P) and/or microsatellite stable (MSS) CRC has also been observed. We sought to characterize MMR-P/MSS CRC among patients with LS.

METHODS

Patients with solid tumors with germline MMR pathogenic/likely pathogenic (P/LP) variants were identified on a prospective matched tumor-normal next-generation sequencing (NGS) protocol. CRCs were evaluated for MMR-D via immunohistochemical (IHC) staining and/or MSI via NGS. Clinical variables were correlated with MMR status using nonparametric tests.

RESULTS

Among 17,617 patients with solid tumors, 1.4% (n = 242) had LS. A total of 36% (86 of 242) of patients with LS had at least one CRC that underwent NGS profiling, amounting to 99 pooled CRCs assessed. A total of 10% (10 of 99) of CRCs were MMR-P, with 100% concordance between MSS status and retained MMR protein staining. A total of 89% (8 of 9) of patients in the MMR-P group had MSH6 or PMS2 variants, compared with 30% (23 of 77) in the MMR-D group (P = .001). A total of 46% (6 of 13) of PMS2+ patients had MMR-P CRC. The median age of onset was 58 and 43 years for MMR-P and MMR-D CRC, respectively (P = .07). Despite the later median age of onset, 40% (4 of 10) of MMR-P CRCs were diagnosed <50. A total of 60% (6 of 10) of MMR-P CRCs were metastatic compared with 13% (12 of 89) of MMR-D CRCs (P = .002). A total of 33% (3 of 9) of patients with MMR-P CRC did not meet LS testing criteria.

CONCLUSION

Patients with LS remained at risk for MMR-P CRC, which was more prevalent among patients with MSH6 and PMS2 variants. MMR-P CRC was later onset and more commonly metastatic compared with MMR-D CRC. Confirmation of tumor MMR/MSI status is critical for patient management and familial risk estimation.

Characteristics of Mismatch Repair-Deficient Colon Cancer in Relation to Mismatch Repair Protein Loss, Hypermethylation Silencing, and Constitutional and Biallelic Somatic Mismatch Repair Gene Pathogenic Variants

BACKGROUND

Mismatch repair-deficient colon cancer is heterogeneous. Differentiating inherited constitutional variants from somatic genetic alterations and gene silencing is important for surveillance and genetic counseling.

OBJECTIVE

This study aimed to determine the extent to which the underlying mechanism of loss of mismatch repair influences molecular and clinicopathologic features of microsatellite instability-high colon cancer.

DESIGN

This is a retrospective analysis.

SETTINGS

This study was conducted at a comprehensive cancer center.

PATIENTS

Patients with microsatellite instability-high colon cancer of stage I, II, or III were included.

INTERVENTION

Patients underwent a curative surgical resection.

MAIN OUTCOME MEASURES

The main outcome measures were hypermethylation of the MLH1 promoter, biallelic inactivation, constitutional pathogenic variants, and loss of specific mismatch repair proteins.

RESULTS

Of the 157 identified tumors with complete genetic analysis, 66% had hypermethylation of the MLH1 promoter, 18% had constitutional pathogenic variants, (Lynch syndrome), 11% had biallelic somatic mismatch repair gene pathogenic variants, and 6% had unexplained high microsatellite instability. The distribution of mismatch repair loss was as follows: MLH1 and PMS2 co-loss, 79% of the tumors; MSH2 and MSH6 co-loss, 10%; MSH6 alone, 3%; PMS2 alone, 2%; other combinations, 2%; no loss, 2%. Tumor mutational burden was lowest in MLH1- and PMS2-deficient tumors. MSH6-deficient tumors had the lowest levels of tumor-infiltrating lymphocytes, lowest MSI scores, and fewest frameshift deletions. Patients with MLH1 promoter hypermethylation were significantly more likely to be older and female and to have right-sided colon lesions than patients with biallelic inactivation. Mutation was the most prevalent second hit in tumors with biallelic inactivation and tumors of patients with Lynch syndrome.

LIMITATIONS

This study was limited by potential selection or referral bias, missing data for some patients, and relatively small sizes of some subgroups.

CONCLUSIONS

Clinical characteristics of mismatch repair-deficient colon cancer vary with the etiology of microsatellite instability, and its molecular characteristics vary with the affected mismatch repair protein. See Video Abstract at http://links.lww.com/DCR/B984 .

CARACTERSTICAS DEL CNCER DE COLON CON DEFICIENCIA EN LA REPARACIN DE ERRORES DE EMPAREJAMIENTO EN RELACIN CON LA PRDIDA DE PROTENAS MMR, SILENCIAMIENTO DE LA HIPERMETILACIN Y LAS VARIANTES PATGENAS SOMTICAS DE GENES MMR CONSTITUCIONAL Y BIALLICO

ANTECEDENTES:El cáncer de colon deficiente en la reparación de errores de emparejamiento es heterogéneo. La diferenciación de las variantes constitucionales heredadas de las alteraciones genéticas somáticas y el silenciamiento de genes es importante para la vigilancia y el asesoramiento genético.OBJETIVO:Determinar hasta qué punto el mecanismo subyacente de pérdida de reparación de desajustes influye en las características moleculares y clinicopatológicas del cáncer de colon con alta inestabilidad de microsatélites.DISEÑO:Análisis retrospectivo.ESCENARIO:Centro integral de cáncer.PACIENTES:Pacientes con cáncer de colon con inestabilidad de microsatélites alta en estadio I, II, o III.INTERVENCIÓN:Resección quirúrgica con intención curativa.PRINCIPALES RESULTADOS Y MEDIDAS:Hipermetilación del promotor MLH1, inactivación bialélica, variante patógena constitucional y pérdida de proteínas específicas reparadoras de desajustes.RESULTADOS:De los 157 tumores identificados con un análisis genético completo, el 66 % tenía hipermetilación del promotor MLH1, el 18 % tenía una variante patogénica constitucional (síndrome de Lynch), el 11 % tenía variantes patogénicas somáticas bialélicas de algún gen MMR y el 6 % tenía una alta inestabilidad de microsatélites sin explicación. La distribución de la pérdida según la proteína de reparación del desajuste fue la siguiente: pérdida conjunta de MLH1 y PMS2, 79 % de los tumores; co-pérdida de MSH2 y MSH6, 10%; MSH6 solo, 3%; PMS2 solo, 2%; otras combinaciones, 2%; sin pérdida, 2%. La carga mutacional del tumor fue más baja en los tumores deficientes en MLH1 y PMS2. Los tumores con deficiencia de MSH6 tenían los niveles más bajos de linfocitos infiltrantes de tumores, las puntuaciones más bajas del sensor de IMS y la menor cantidad de deleciones por cambio de marco. Los pacientes con hipermetilación del promotor MLH1 tenían significativamente más probabilidades de ser mayores y mujeres y de tener lesiones en el colon derecho que los pacientes con inactivación bialélica. La mutación fue el segundo golpe más frecuente en tumores con inactivación bialélica y tumores de pacientes con síndrome de Lynch.LIMITACIONES:Sesgo potencial de selección o referencia, datos faltantes para algunos pacientes y tamaños relativamente pequeños de algunos subgrupos.CONCLUSIONES:Las características clínicas del cáncer de colon deficiente en reparación de desajustes varían con la etiología de la inestabilidad de microsatélites, y sus características moleculares varían con la proteína de reparación de desajustes afectada. Vea Resumen de video en http://links.lww.com/DCR/B984 . (Traducción-Dr. Felipe Bellolio ).

Molecular Classification of Appendiceal Adenocarcinoma

PURPOSE

Appendiceal adenocarcinomas (ACs) are rare, histologically diverse malignancies treated as colorectal cancers despite having distinct biology and clinical behavior. To guide clinical decision making, we defined molecular subtypes of AC associated with patient survival, metastatic burden, and chemotherapy response.

PATIENTS AND METHODS

A comprehensive molecular analysis was performed in patients with AC to define molecular subtypes. Associations between molecular subtype and overall survival, intraoperative peritoneal cancer index, and first-line chemotherapy response were assessed adjusting for histopathologic and clinical variables using multivariable Cox proportional hazards, linear regression, and logistic regression models.

RESULTS

We defined distinct molecular lineages of mucinous appendiceal adenocarcinoma (MAAP) from co-occurring mutations in GNAS, RAS, and TP53. Of 164 MAAP tumors, 24 were RAS-mutant (mut) predominant (RAS-mut/GNAS-wild-type [wt]/TP53-wt) with significantly decreased mutations and chromosomal alterations compared with tumors with GNAS mutations (GNAS-mut predominant) or TP53 mutations (TP53-mut predominant). No patient with RAS-mut predominant subtype metastatic MAAP died of cancer, and overall survival in this subgroup was significantly improved compared with patients with GNAS-mut (P = .05) and TP53-mut (P = .004) predominant subtypes. TP53-mut predominant subtypes were highly aneuploid; increased tumor aneuploidy was independently (P = .001) associated with poor prognosis. The findings retained significance in patients with any metastatic AC. RAS-mut predominant metastases exhibited reduced peritoneal tumor bulk (P = .04) and stromal invasion (P < .001) compared with GNAS-mut or TP53-mut predominant tumors, respectively. Patients with RAS-mut predominant MAAP responded more to first-line chemotherapy (50%) compared with patients with GNAS-mut predominant tumors (6%, P = .03).

CONCLUSION

AC molecular patterns identify distinct molecular subtypes: a clinically indolent RAS-mut/GNAS-wt/TP53-wt subtype; a chemotherapy-resistant GNAS-mut predominant subtype; and an aggressive, highly aneuploid TP53-mut predominant subtype. Each subtype exhibits conserved clinical behavior irrespective of histopathology.

Circulating tumor DNA (ctDNA) for response assessment in patients with anal cancer treated with definitive chemoradiation

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Background: We hypothesized that circulating tumor DNA (ctDNA) clearance could provide an early signal for clinical complete response (cCR) and/ or long-term recurrence compared to standard clinical exam modalities in patients with anal squamous cell carcinoma (ASCC) undergoing definitive chemoradiation (CRT). Methods: Since early 2021 patients with ASCC undergoing CRT at 2 institutions were offered ctDNA monitoring with a commercially available tumor-bespoke multiplex PCR assay. All patients provided written informed consent for ctDNA testing. Patients were clinically restaged, 3-4 months post-CRT, by clinical exam, endoscopy, and/ or MRI and annually with CT chest, abdomen, and pelvis. cCR was defined as no tumor by digital exam, endoscopy and/or MRI. Molecular ctDNA response is described according to cCR, tumor recurrence, and survival. Results: From January 2021 to September 2022, 31 patients with ASCC treated with definitive CRT underwent ctDNA response assessment. The majority (68%) of patients had stage III disease. Patients were treated to a median radiation dose of 54Gy in 27 fractions with combinatorial mitomycin and fluoropyrimidine-based chemotherapy in 94%, and fluoropyrimidine-based chemotherapy alone in 6%. The median follow up was 22 weeks. ctDNA testing was performed in 25 of these patients at baseline, 26 patients during CRT, and 20 patients 30-days post-CRT. At baseline 88% of patients had detectable ctDNA. Patients with stage III, as compared to stage I-II, disease had numerically higher baseline ctDNA levels (26 vs 4 mean tumor molecules per milliliter (MTM/mL), p=0.08). ctDNA levels decreased with treatment (19 vs 0.9 MTM/mL, p=0.05) among the 18 patients with detectable ctDNA and ctDNA tested during CRT, with 50% of patients entering molecular remission. Similarly, ctDNA levels decreased (21 vs 0.2 MTM/mL, p=0.05) among the 16 patients with detectable ctDNA and ctDNA tested post-CRT, with 94% entering molecular remission. All patients in molecular remission were confirmed to have a cCR. Time to molecular ctDNA remission was significantly shorter than time to cCR (median 30 vs 135 days, p <0.01). There were no molecular recurrences among the 16, 14, and 7 patients with ctDNA testing at 2-4 months, 4-8 months, and 8-12 months post-CRT. All patients are alive and without clinical/ radiographic evidence of disease. Conclusions: Surveillance ctDNA monitoring may provide an earlier response assessment for patients with ASCC undergoing CRT compared to standard clinical measures. Longer term follow-up is required to determine if ctDNA response correlates with long term recurrence free survival. Larger trials are needed to assess the clinical utility of integrating molecular ctDNA response in therapeutic response surveillance.

Genomic landscape of acquired resistance to targeted therapies in metastatic colorectal cancer (mCRC)

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Background: Therapies targeting oncogenic driver mutations have radically altered the treatment paradigm for mCRC and improved outcomes. New selective inhibitors aim to expand the portion of mCRC with targetable alterations. However, these drugs are limited by a relatively short duration of response before the emergence of acquired resistance. We hypothesized that both the putative resistance mechanism (mutations (MUT) versus copy number alterations (CNA)) and the clonality of the emergent mutations may influence time to resistance. Methods: We screened the MSKCC IMPACT dataset of 5,403 MSS (microsatellite stable) CRC patient samples (3,704 primary sequenced, 1669 metastatic site sequenced) for patients (pts) who had been treated with targeted therapies against EGFR, BRAF, KRAS G12C, or HER2 with tissue or liquid biopsy samples profiled at progression. Clinicopathological features and acquired genomic changes emerging at resistance were assessed. Results: 42 pts were identified with targeted oncogenic drivers consisting of BRAF V600E (17 pts), EGFR (12 pts), KRAS G12C (11 pts), and HER2 (2 pts). Progression specimens analyzed consisted of tissue biopsies in 17 pts (40%) and circulating free DNA (cfDNA) in 21 pts (50%), 4 pts had both tissue and cfDNA analyzed at progression. Median time on targeted therapy (TOT) was 7.1 months (95% CI: 5.6-8.5). Putative resistance alterations were identified in 33 pts (79%) (18 cfDNA, 11 tissue, 4 both cfDNA and tissue) and consisted of MUT alone in 30%, MUT+CNA or rearrangement 70%. Concurrent PIK3CA mutations in pre-treatment tissues were identified in 17 pts (40%) and did not associate with TOT (p=0.68); acquired PI3K pathway alterations were identified in 5 pts (12%), including 2 pts who had baseline tumor PIK3CA mutation. Number of putative resistance alterations ranged from 0-13, with multiple resistance alterations identified in 18 pts (15 ctDNA, 3 tissue), and these could be categorized into three groups: one alteration (15/33; 45%), 2-4 alterations (8/33; 24%), and ≥5 alterations (10/33; 30%). Evaluating TOT by type of alteration: MUT only: 9.8 months, MUT+ CNA+/- rearrangement: 6.6 months (p=0.0079). Evaluating TOT by number of alterations: >4 alterations: 6.1 months versus 1-4 alterations: 8.9 months (p=0.012), or 1 alteration: 8.0 months versus >1 alteration: 6.7months (p= 0.5). There was no significant difference in TOT when evaluating by clonality of mutations, where subclonal was defined as <5% of highest variant allelic fraction (clonal vs subclonal, 9.7 vs 6.7 months, p= 0.09). Fusions identified at time of resistance (involving BRAF in 2 pts, MET in 1 pt, RET in 1 pt) occurred with ≥5 alterations in 3 of 4 pts. Conclusions: Presence of CNA and ≥5 new alterations at resistance were associated with shorter TOT, and there was a trend for subclonal alterations and shorter TOT. New approaches that target underlying mechanisms for these changes may extend TOT.

KRAS inhibition in metastatic colorectal cancer: An update

About half of colorectal cancers harbor mutations in the KRAS gene. The presence of these mutations is associated with worse prognosis and, until now, the absence of matched targeted therapy options. In this review, we discuss clinical efforts to target KRAS in colorectal cancer from studies of downstream inhibitors to recent direct inhibitors of KRASG12C and other KRAS mutants. Early clinical trial data, however, suggest more limited activity for these novel inhibitors in colorectal cancer compared to other cancer types, and we discuss the role of receptor tyrosine kinase signaling and parallel signaling pathways in modulating response to these inhibitors. We also review the effect of KRAS mutations on the tumor-immune microenvironment and efforts to induce an immune response against these tumors.

Clinical Importance of Clonal Hematopoiesis in Metastatic Gastrointestinal Tract Cancers

Importance

Clonal hematopoiesis (CH) has been associated with development of atherosclerosis and leukemia and worse survival among patients with cancer; however, the association with cancer therapy efficacy, in particular immune checkpoint blockade (ICB), and toxicity has not yet been established. Given the widespread use of ICB and the critical role hematopoietic stem cell-derived lymphocytes play in mediating antitumor responses, CH may be associated with therapeutic efficacy and hematologic toxicity.

Objective

To determine the association between CH and outcomes, hematologic toxicity, and therapeutic efficacy in patients with metastatic gastrointestinal tract cancers being treated with systemic therapy, both in the first-line metastatic treatment setting and in ICB.

Design, Setting, and Participants

This retrospective cohort study included 633 patients with stage IV colorectal (CRC) and esophagogastric (EGC) cancer who were treated with first-line chemotherapy and/or ICB at Memorial Sloan Kettering Cancer Center. Patients underwent matched tumor and peripheral blood DNA sequencing using the Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets next-generation sequencing assay between January 1, 2006, and December 31, 2020.

Exposures

Clonal hematopoiesis-related genetic alterations were identified by next-generation sequencing of patients' tumor and normal blood buffy coat samples, with a subset of these CH alterations annotated as likely putative drivers (CH-PD) based upon previously established criteria.

Main Outcomes and Measures

Patients with CH and CH-PD in peripheral blood samples were identified, and these findings were correlated with survival outcomes (progression-free survival [PFS] and overall survival [OS]) during first-line chemotherapy and ICB, as well as baseline white blood cell levels and the need for granulocyte colony-stimulating factor (G-CSF) support.

Results

Among the 633 patients included in the study (390 men [61.6%]; median age, 58 [IQR, 48-66] years), the median age was 52 (IQR, 45-63) years in the CRC group and 61 (IQR, 53-69) years in the EGC group. In the CRC group, 161 of 301 patients (53.5%) were men, compared with 229 of 332 patients (69.0%) in the EGC group. Overall, 62 patients (9.8%) were Asian, 45 (7.1%) were Black or African American, 482 (76.1%) were White, and 44 (7.0%) were of unknown race or ethnicity. Presence of CH was identified in 115 patients with EGC (34.6%) and 83 with CRC (27.6%), with approximately half of these patients harboring CH-PD (CRC group, 44 of 83 [53.0%]; EGC group, 55 of 115 [47.8%]). Patients with EGC and CH-PD exhibited a significantly worse median OS of 16.0 (95% CI, 11.6-22.3) months compared with 21.6 (95% CI, 19.6-24.3) months for those without CH-PD (P = .01). For patients with CRC and EGC, CH and CH-PD were not associated with PFS differences in patients undergoing ICB or first-line chemotherapy. Neither CH nor CH-PD were correlated with baseline leukocyte levels or increased need for G-CSF support.

Conclusions and Relevance

These findings suggest CH and CH-PD are not directly associated with the treatment course of patients with metastatic gastrointestinal tract cancer receiving cancer-directed therapy.

BREAKWATER safety lead-in (SLI): Encorafenib (E) + cetuximab (C) + chemotherapy for BRAFV600E metastatic colorectal cancer (mCRC)

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Background: Based on the phase 3 BEACON study (NCT02928224), BRAF inhibitor (i) encorafenib (E) + EGFRi cetuximab (C) was approved for the treatment (tx) of previously treated patients (pts) with BRAFV600E mCRC, with mPFS of 4.3 months (mo) and ORR of 19.5%. In the phase 2 ANCHOR study (NCT03693170), mPFS was 5.8 mo and ORR was 48% for 1L EC + binimetinib in BRAFV600E mCRC. To further assess 1L approaches, the ongoing phase 3 BREAKWATER study (NCT04607421) is evaluating EC ± chemotherapy vs standard-of-care chemotherapy in BRAFV600E mCRC. Here, we present updated safety and antitumor activity data as well as biomarker data from the BREAKWATER SLI. Methods: Inclusion criteria for the SLI were BRAFV600E mCRC (blood or tumor tissue), ≤1 prior systemic tx for mCRC, and ECOG PS 0/1. Pts previously treated with BRAFi/EGFRi or both oxaliplatin and irinotecan were excluded. Pts received E 300 mg daily + C 500 mg/m2 every 2 weeks (Q2W) + either mFOLFOX6 Q2W (n=27) or FOLFIRI Q2W (n=30) in 28-day cycles until disease progression or unacceptable toxicity. The primary endpoint was frequency of dose-limiting toxicities. Secondary endpoints included safety, pharmacokinetics, and antitumor activity. Exploratory endpoints included evaluation of plasma (circulating tumor DNA [ctDNA] genomic profiling) and tumor tissue (molecular profiling) biomarkers. Updated results from the BREAKWATER SLI will be presented, including overall safety and tolerability and antitumor activity. Biomarker data, including changes from baseline in BRAFV600E ctDNA following treatment (Cycle 1 Day 15, Cycle 2 Day 15 and Cycle 7 Day 1) and MSI status of pts, will also be presented. Expected conclusions will be included in the final abstract. Clinical trial information: NCT04607421 .

Molecular Characterization of Acquired Resistance to KRASG12C-EGFR Inhibition in Colorectal Cancer

With the combination of KRASG12C and EGFR inhibitors, KRAS is becoming a druggable target in colorectal cancer. However, secondary resistance limits its efficacy. Using cell lines, patient-derived xenografts, and patient samples, we detected a heterogeneous pattern of putative resistance alterations expected primarily to prevent inhibition of ERK signaling by drugs at progression. Serial analysis of patient blood samples on treatment demonstrates that most of these alterations are detected at a low frequency except for KRASG12C amplification, a recurrent resistance mechanism that rises in step with clinical progression. Upon drug withdrawal, resistant cells with KRASG12C amplification undergo oncogene-induced senescence, and progressing patients experience a rapid fall in levels of this alteration in circulating DNA. In this new state, drug resumption is ineffective as mTOR signaling is elevated. However, our work exposes a potential therapeutic vulnerability, whereby therapies that target the senescence response may overcome acquired resistance.

SIGNIFICANCE

Clinical resistance to KRASG12C-EGFR inhibition primarily prevents suppression of ERK signaling. Most resistance mechanisms are subclonal, whereas KRASG12C amplification rises over time to drive a higher portion of resistance. This recurrent resistance mechanism leads to oncogene-induced senescence upon drug withdrawal and creates a potential vulnerability to senolytic approaches. This article is highlighted in the In This Issue feature, p. 1.

Integrated clinical and genomic analysis identifies driver events and molecular evolution of colitis-associated cancers

Inflammation has long been recognized to contribute to cancer development, particularly across the gastrointestinal tract. Patients with inflammatory bowel disease have an increased risk for bowel cancers, and it has been posited that a field of genetic changes may underlie this risk. Here, we define the clinical features, genomic landscape, and germline alterations in 174 patients with colitis-associated cancers and sequenced 29 synchronous or isolated dysplasia. TP53 alterations, an early and highly recurrent event in colitis-associated cancers, occur in half of dysplasia, largely as convergent evolution of independent events. Wnt pathway alterations are infrequent, and our data suggest transcriptional rewiring away from Wnt. Sequencing of multiple dysplasia/cancer lesions from mouse models and patients demonstrates rare shared alterations between lesions. These findings suggest neoplastic bowel lesions developing in a background of inflammation experience lineage plasticity away from Wnt activation early during tumorigenesis and largely occur as genetically independent events.

Adagrasib with or without Cetuximab in Colorectal Cancer with Mutated KRAS G12C

BACKGROUND

Adagrasib, an oral small-molecule inhibitor of mutant KRAS G12C protein, has shown clinical activity in pretreated patients with several tumor types, including colorectal cancer. Preclinical studies suggest that combining a KRAS G12C inhibitor with an epidermal growth factor receptor antibody could be an effective clinical strategy.

METHODS

In this phase 1-2, open-label, nonrandomized clinical trial, we assigned heavily pretreated patients with metastatic colorectal cancer with mutant KRAS G12C to receive adagrasib monotherapy (600 mg orally twice daily) or adagrasib (at the same dose) in combination with intravenous cetuximab once a week (with an initial loading dose of 400 mg per square meter of body-surface area, followed by a dose of 250 mg per square meter) or every 2 weeks (with a dose of 500 mg per square meter). The primary end points were objective response (complete or partial response) and safety.

RESULTS

As of June 16, 2022, a total of 44 patients had received adagrasib, and 32 had received combination therapy with adagrasib and cetuximab, with a median follow-up of 20.1 months and 17.5 months, respectively. In the monotherapy group (43 evaluable patients), a response was reported in 19% of the patients (95% confidence interval [CI], 8 to 33). The median response duration was 4.3 months (95% CI, 2.3 to 8.3), and the median progression-free survival was 5.6 months (95% CI, 4.1 to 8.3). In the combination-therapy group (28 evaluable patients), the response was 46% (95% CI, 28 to 66). The median response duration was 7.6 months (95% CI, 5.7 to not estimable), and the median progression-free survival was 6.9 months (95% CI, 5.4 to 8.1). The percentage of grade 3 or 4 treatment-related adverse events was 34% in the monotherapy group and 16% in the combination-therapy group. No grade 5 adverse events were observed.

CONCLUSIONS

Adagrasib had antitumor activity in heavily pretreated patients with metastatic colorectal cancer with mutant KRAS G12C, both as oral monotherapy and in combination with cetuximab. The median response duration was more than 6 months in the combination-therapy group. Reversible adverse events were common in the two groups. (Funded by Mirati Therapeutics; KRYSTAL-1 ClinicalTrials.gov number, NCT03785249.).

Sotorasib in KRAS p.G12C-Mutated Advanced Pancreatic Cancer

BACKGROUND

KRAS p.G12C mutation occurs in approximately 1 to 2% of pancreatic cancers. The safety and efficacy of sotorasib, a KRAS G12C inhibitor, in previously treated patients with KRAS p.G12C-mutated pancreatic cancer are unknown.

METHODS

We conducted a single-group, phase 1-2 trial to assess the safety and efficacy of sotorasib treatment in patients with KRAS p.G12C-mutated pancreatic cancer who had received at least one previous systemic therapy. The primary objective of phase 1 was to assess safety and to identify the recommended dose for phase 2. In phase 2, patients received sotorasib at a dose of 960 mg orally once daily. The primary end point for phase 2 was a centrally confirmed objective response (defined as a complete or partial response). Efficacy end points were assessed in the pooled population from both phases and included objective response, duration of response, time to objective response, disease control (defined as an objective response or stable disease), progression-free survival, and overall survival. Safety was also assessed.

RESULTS

The pooled population from phases 1 and 2 consisted of 38 patients, all of whom had metastatic disease at enrollment and had previously received chemotherapy. At baseline, patients had received a median of 2 lines (range, 1 to 8) of therapy previously. All 38 patients received sotorasib in the trial. A total of 8 patients had a centrally confirmed objective response (21%; 95% confidence interval [CI], 10 to 37). The median progression-free survival was 4.0 months (95% CI, 2.8 to 5.6), and the median overall survival was 6.9 months (95% CI, 5.0 to 9.1). Treatment-related adverse events of any grade were reported in 16 patients (42%); 6 patients (16%) had grade 3 adverse events. No treatment-related adverse events were fatal or led to treatment discontinuation.

CONCLUSIONS

Sotorasib showed anticancer activity and had an acceptable safety profile in patients with KRAS p.G12C-mutated advanced pancreatic cancer who had received previous treatment. (Funded by Amgen and others; CodeBreaK 100 ClinicalTrials.gov number, NCT03600883.).

Abstract A005: Genomic profiling identifies differences in the distribution of APC mutations in non-Hispanic black and non-Hispanic white patients with colorectal cancer

Intro: We compared molecular profiles of a large cohort of colorectal cancer patients treated at a single tertiary center to better understand the role of genomic factors for explaining differences in clinical outcomes of non-Hispanic black (NHB) vs. non-Hispanic white (NHW) patients. Methods: We analyzed targeted DNA sequencing data from 4,322 colorectal adenocarcinoma patients treated at Memorial Sloan Kettering Cancer Center, including 366 patients self-identified as NHB and 3,956 patients who self-identified as NHW. Tumors were sequenced using the MSK-IMPACT assay, a targeted sequencing platform that identifies somatic mutations, copy number changes, and gene fusions in a selected panel of 341-505 genes in tumor tissue compared to a matched normal blood sample. Genetic ancestry was estimated using reference populations from the 1000 Genomes Project, including European (EUR), African (AFR), East Asian (EAS), South Asian (SAS), and Native American (NAM). Patients were assigned specific ancestry labels when the corresponding ancestry fraction was above 80%. Results: Self-reported race and genetic ancestry were highly concordant, with 225/235, 95.7% of AFR patients self-reporting as NHB and 3215/3216, 99.96% of EUR patients self-reporting as NHW. While tumors from AFR patients were more often located in the right colon (43.27% vs. 30.56%, p&lt;0.001), they were also found to be less frequently microsatellite-instable (MSI) when compared to tumors from EUR patients (5.96% vs. 11.1%, p=0.026). Among right-sided cases, MSI tumors accounted only for 7.8% of AFR patients vs. 26.4% in EUR cases (p&lt;0.0001). Among MSS cases, tumors from AFR patients had a higher frequency of KRAS (59.1% vs. 44.7%, p&lt;0.0001) and SMAD2 (7.72% vs. 3.59%, p=0.006) mutations, as well as a lower frequency of BRAF mutations (3.18% vs. 7.22%, p=0.019). While the frequency of APC mutations was similar in both groups (77.45% vs. 72.98%, p=0.147), APC mutations in tumors from AFR patients were more frequently located within the C-terminal part of the protein (i.e., beyond the first 1400 amino acids), both when all tumors were analyzed together (50.0% vs. 38.5%, p=0.003) and when the analysis was restricted to non-hypermutated, microsatellite-stable (MSS) cases (48.0% vs. 35.5%, p=0.001). This higher frequency of C-terminal side mutations was also seen in self-reported Black/African American MSS colorectal cancer patients from AACR Project GENIE (58.9% vs 41.3%, p &lt; 0.001) and The Cancer Genome Atlas (61.1% vs 40%, p = 0.026). This type of distal APC mutations, which are considered “weak activators” of Wnt signaling, have been linked to more aggressive tumors due to concurrent activation of alternative mitogenic pathways such as ERK or PI3K. Conclusion: Some of the genomic differences between NHB and NHW patients that we had previously identified based on self-reported race were confirmed using analyses of genetic ancestry. We also present preliminary data demonstrating racial differences in the distribution of inactivating somatic mutations within the APC gene.

Citation Format: Henry Walch, Anisha Luthra, Walid Chatila, Kanika Arora, Samantha Chin, Michele Waters, Jesse J. Smith, Nikolaus Schultz, Michael F. Berger, Karuna Ganesh, Julio Garcia-Aguilar, Rona Yaeger, Francisco Sanchez-Vega. Genomic profiling identifies differences in the distribution of APC mutations in non-Hispanic black and non-Hispanic white patients with colorectal cancer [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer; 2022 Oct 1-4; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_1):Abstract nr A005.

Molecular Pathways and Mechanisms of BRAF in Cancer Therapy

With the identification of activating mutations in BRAF across a wide variety of malignancies, substantial effort was placed in designing safe and effective therapeutic strategies to target BRAF. These efforts have led to the development and regulatory approval of three BRAF inhibitors as well as five combinations of a BRAF inhibitor plus an additional agent(s) to manage cancer such as melanoma, non-small cell lung cancer, anaplastic thyroid cancer, and colorectal cancer. To date, each regimen is effective only in patients with tumors harboring BRAFV600 mutations and the duration of benefit is often short-lived. Further limitations preventing optimal management of BRAF-mutant malignancies are that treatments of non-V600 BRAF mutations have been less profound and combination therapy is likely necessary to overcome resistance mechanisms, but multi-drug regimens are often too toxic. With the emergence of a deeper understanding of how BRAF mutations signal through the RAS/MAPK pathway, newer RAF inhibitors are being developed that may be more effective and potentially safer and more rational combination therapies are being tested in the clinic. In this review, we identify the mechanics of RAF signaling through the RAS/MAPK pathway, present existing data on single-agent and combination RAF targeting efforts, describe emerging combinations, summarize the toxicity of the various agents in clinical testing, and speculate as to where the field may be headed.

Natural Language Processing of Computed Tomography Reports to Label Metastatic Phenotypes With Prognostic Significance in Patients With Colorectal Cancer

PURPOSE

Natural language processing (NLP) applied to radiology reports can help identify clinically relevant M1 subcategories of patients with colorectal cancer (CRC). The primary purpose was to compare the overall survival (OS) of CRC according to American Joint Committee on Cancer TNM staging and explore an alternative classification. The secondary objective was to estimate the frequency of metastasis for each organ.

METHODS

Retrospective study of CRC who underwent computed tomography (CT) chest, abdomen, and pelvis between July 1, 2009, and March 26, 2019, at a tertiary cancer center, previously labeled for the presence or absence of metastasis by an NLP prediction model. Patients were classified in M0, M1a, M1b, and M1c (American Joint Committee on Cancer), or an alternative classification on the basis of the metastasis organ number: M1, single; M2, two; M3, three or more organs. Cox regression models were used to estimate hazard ratios; Kaplan-Meier curves were used to visualize survival curves using the two M1 subclassifications.

RESULTS

Nine thousand nine hundred twenty-eight patients with a total of 48,408 CT chest, abdomen, and pelvis reports were included. On the basis of NLP prediction, the median OS of M1a, M1b, and M1c was 4.47, 1.72, and 1.52 years, respectively. The median OS of M1, M2, and M3 was 4.24, 2.05, and 1.04 years, respectively. Metastases occurred most often in liver (35.8%), abdominopelvic lymph nodes (32.9%), lungs (29.3%), peritoneum (22.0%), thoracic nodes (19.9%), bones (9.2%), and pelvic organs (7.5%). Spleen and adrenal metastases occurred in < 5%.

CONCLUSION

NLP applied to a large radiology report database can identify clinically relevant metastatic phenotypes and be used to investigate new M1 substaging for CRC. Patients with three or more metastatic disease organs have the worst prognosis, with an OS of 1 year.

BRAF-Mutated Advanced Colorectal Cancer: A Rapidly Changing Therapeutic Landscape

BRAF-mutated advanced colorectal cancer is a relatively small but critical subset of this tumor type on the basis of prognostic and predictive implications. BRAF alterations in colorectal cancer are classified into three functional categories on the basis of signaling mechanisms, with the class I BRAFV600E mutation occurring most frequently in colorectal cancer. Functional categorization of BRAF mutations in colorectal cancer demonstrates distinct mitogen-activated protein kinase pathway signaling. On the basis of recent clinical trials, current standard-of-care therapies for patients with BRAFV600E-mutated metastatic colorectal cancer include first-line cytotoxic chemotherapy plus bevacizumab and subsequent therapy with the BRAF inhibitor encorafenib and antiepidermal growth factor receptor antibody cetuximab. Treatment regimens currently under exploration in BRAFV600E-mutant metastatic colorectal cancer include combinatorial options of various pathway-targeted therapies, cytotoxic chemotherapy, and/or immune checkpoint blockade, among others. Circumvention of adaptive and acquired resistance to BRAF-targeted therapies is a significant challenge to be overcome in BRAF-mutated advanced colorectal cancer.

Organ Preservation in Patients With Rectal Adenocarcinoma Treated With Total Neoadjuvant Therapy

PURPOSE

Prospective data on the efficacy of a watch-and-wait strategy to achieve organ preservation in patients with locally advanced rectal cancer treated with total neoadjuvant therapy are limited.

METHODS

In this prospective, randomized phase II trial, we assessed the outcomes of 324 patients with stage II or III rectal adenocarcinoma treated with induction chemotherapy followed by chemoradiotherapy (INCT-CRT) or chemoradiotherapy followed by consolidation chemotherapy (CRT-CNCT) and either total mesorectal excision (TME) or watch-and-wait on the basis of tumor response. Patients in both groups received 4 months of infusional fluorouracil-leucovorin-oxaliplatin or capecitabine-oxaliplatin and 5,000 to 5,600 cGy of radiation combined with either continuous infusion fluorouracil or capecitabine during radiotherapy. The trial was designed as two stand-alone studies with disease-free survival (DFS) as the primary end point for both groups, with a comparison to a null hypothesis on the basis of historical data. The secondary end point was TME-free survival.

RESULTS

Median follow-up was 3 years. Three-year DFS was 76% (95% CI, 69 to 84) for the INCT-CRT group and 76% (95% CI, 69 to 83) for the CRT-CNCT group, in line with the 3-year DFS rate (75%) observed historically. Three-year TME-free survival was 41% (95% CI, 33 to 50) in the INCT-CRT group and 53% (95% CI, 45 to 62) in the CRT-CNCT group. No differences were found between groups in local recurrence-free survival, distant metastasis-free survival, or overall survival. Patients who underwent TME after restaging and patients who underwent TME after regrowth had similar DFS rates.

CONCLUSION

Organ preservation is achievable in half of the patients with rectal cancer treated with total neoadjuvant therapy, without an apparent detriment in survival, compared with historical controls treated with chemoradiotherapy, TME, and postoperative chemotherapy.

Organ Preservation in Patients With Rectal Adenocarcinoma Treated With Total Neoadjuvant Therapy

PURPOSE

Prospective data on the efficacy of a watch-and-wait strategy to achieve organ preservation in patients with locally advanced rectal cancer treated with total neoadjuvant therapy are limited.

METHODS

In this prospective, randomized phase II trial, we assessed the outcomes of 324 patients with stage II or III rectal adenocarcinoma treated with induction chemotherapy followed by chemoradiotherapy (INCT-CRT) or chemoradiotherapy followed by consolidation chemotherapy (CRT-CNCT) and either total mesorectal excision (TME) or watch-and-wait on the basis of tumor response. Patients in both groups received 4 months of infusional fluorouracil-leucovorin-oxaliplatin or capecitabine-oxaliplatin and 5,000 to 5,600 cGy of radiation combined with either continuous infusion fluorouracil or capecitabine during radiotherapy. The trial was designed as two stand-alone studies with disease-free survival (DFS) as the primary end point for both groups, with a comparison to a null hypothesis on the basis of historical data. The secondary end point was TME-free survival.

RESULTS

Median follow-up was 3 years. Three-year DFS was 76% (95% CI, 69 to 84) for the INCT-CRT group and 76% (95% CI, 69 to 83) for the CRT-CNCT group, in line with the 3-year DFS rate (75%) observed historically. Three-year TME-free survival was 41% (95% CI, 33 to 50) in the INCT-CRT group and 53% (95% CI, 45 to 62) in the CRT-CNCT group. No differences were found between groups in local recurrence-free survival, distant metastasis-free survival, or overall survival. Patients who underwent TME after restaging and patients who underwent TME after regrowth had similar DFS rates.

CONCLUSION

Organ preservation is achievable in half of the patients with rectal cancer treated with total neoadjuvant therapy, without an apparent detriment in survival, compared with historical controls treated with chemoradiotherapy, TME, and postoperative chemotherapy.

PD-1 Blockade in Mismatch Repair-Deficient, Locally Advanced Rectal Cancer

BACKGROUND

Neoadjuvant chemotherapy and radiation followed by surgical resection of the rectum is a standard treatment for locally advanced rectal cancer. A subset of rectal cancer is caused by a deficiency in mismatch repair. Because mismatch repair-deficient colorectal cancer is responsive to programmed death 1 (PD-1) blockade in the context of metastatic disease, it was hypothesized that checkpoint blockade could be effective in patients with mismatch repair-deficient, locally advanced rectal cancer.

METHODS

We initiated a prospective phase 2 study in which single-agent dostarlimab, an anti-PD-1 monoclonal antibody, was administered every 3 weeks for 6 months in patients with mismatch repair-deficient stage II or III rectal adenocarcinoma. This treatment was to be followed by standard chemoradiotherapy and surgery. Patients who had a clinical complete response after completion of dostarlimab therapy would proceed without chemoradiotherapy and surgery. The primary end points are sustained clinical complete response 12 months after completion of dostarlimab therapy or pathological complete response after completion of dostarlimab therapy with or without chemoradiotherapy and overall response to neoadjuvant dostarlimab therapy with or without chemoradiotherapy.

RESULTS

A total of 12 patients have completed treatment with dostarlimab and have undergone at least 6 months of follow-up. All 12 patients (100%; 95% confidence interval, 74 to 100) had a clinical complete response, with no evidence of tumor on magnetic resonance imaging, 18F-fluorodeoxyglucose-positron-emission tomography, endoscopic evaluation, digital rectal examination, or biopsy. At the time of this report, no patients had received chemoradiotherapy or undergone surgery, and no cases of progression or recurrence had been reported during follow-up (range, 6 to 25 months). No adverse events of grade 3 or higher have been reported.

CONCLUSIONS

Mismatch repair-deficient, locally advanced rectal cancer was highly sensitive to single-agent PD-1 blockade. Longer follow-up is needed to assess the duration of response. (Funded by the Simon and Eve Colin Foundation and others; ClinicalTrials.gov number, NCT04165772.).