Mismatch Repair Deficiency Testing in Patients With Colorectal Cancer and Nonadherence to Testing Guidelines in Young Adults

Hereditary Colorectal Cancer Syndromes

OBJECTIVES

To review the most common hereditary colorectal cancer syndromes with known associated mutated genes, associated cancer risks, and current screening and prevention current.

DATA SOURCES

Online search of PubMed, EBSCOhost, and Medline, review of the literature for each syndrome described.

CONCLUSION

Hereditary colon cancer accounts for approximately 10% of all colorectal cancers in the United States. There are multiple hereditary colorectal cancer syndromes known with respective associated genetic mutations, cancer risks, and screening and prevention recommendations.

IMPLICATIONS FOR NURSING PRACTICE

Nurses at all levels of practice need to be knowledgeable about the various hereditary colorectal cancer syndromes to guide appropriate referral to a genetics professional and to provide appropriate care to these high-risk individuals.

Early-onset colorectal cancer in young individuals

Treatment of young adults with colorectal cancer (CRC) represents an unmet clinical need, especially as diagnosis in this population might lead to the greatest loss of years of life. Since 1994, CRC incidence in individuals younger than 50 years has been increasing by 2% per year. The surge in CRC incidence in young adults is particularly alarming as the overall CRC frequency has been decreasing. Early-onset CRC are characterized by a more advanced stage at diagnosis, poorer cell differentiation, higher prevalence of signet ring cell histology, and left colon-sided location of the primary tumor. Among EO-CRC, approximately 30% of patients are affected by tumors harboring mutations causing hereditary cancer predisposing syndromes, and 20% have familial CRC. Most notably, the remaining 50% of EO-CRC patients have neither hereditary syndromes nor familial CRC, thus representing a formidable challenge for research. In this review article we summarize epidemiology, clinical and molecular features, heredity and outcome of treatments of EO-CRC, and provide considerations for future perspectives.

Low Referral Rate for Genetic Testing in Racially and Ethnically Diverse Patients Despite Universal Colorectal Cancer Screening

BACKGROUND & AIMS

Guidelines recommend that all colorectal tumors be assessed for mismatch repair deficiency, which could increase identification of patients with Lynch syndrome. This is of particular importance for minority populations, in whom hereditary syndromes are under diagnosed. We compared rates and outcomes of testing all tumor samples (universal testing) collected from a racially and ethnically diverse population for features of Lynch syndrome.

METHODS

We performed a retrospective analysis of colorectal tumors tested from 2012 through 2016 at 4 academic centers. Tumor samples were collected from 767 patients with colorectal cancer (52% non-Hispanic white [NHW], 26% African American, and 17% Hispanic patients). We assessed rates of tumor testing, recommendations for genetic evaluation, rates of attending a genetic evaluation, and performance of germline testing overall and by race/ethnicity. We performed univariate and multivariate regression analyses.

RESULTS

Overall, 92% of colorectal tumors were analyzed for mismatch repair deficiency without significant differences among races/ethnicities. However, minority patients were significantly less likely to be referred for genetic evaluation (21.2% for NHW patients vs 16.9% for African American patients and 10.9% for Hispanic patients; P = .02). Rates of genetic testing were also lower among minority patients (10.7% for NHW patients vs 6.0% for AA patients and 3.1% for Hispanic patients; P < .01). On multivariate analysis, African American race, older age, and medical center were independently associated with lack of referral for genetic evaluation and genetic testing.

CONCLUSION

In a retrospective analysis, we found that despite similar rates of colorectal tumor analysis, minority patients are less likely to be recommended for genetic evaluation or to undergo germline testing for Lynch syndrome. Improvements in institutional practices in follow up after tumor testing could reduce barriers to diagnosis of Lynch diagnosis in minorities.

Recent Advances in Lynch Syndrome: Diagnosis, Treatment, and Cancer Prevention

Identification of individuals with inherited predispositions to cancer, including Lynch syndrome, can help prevent cancer and cancer-related death by allowing for the uptake of specific cancer prevention and screening as well as the use of therapies directed toward the underlying neoplastic process for individuals with advanced cancer. In the 25 years since the discovery of microsatellite instability (MSI) and the first recognition of germline mismatch repair (MMR) gene variants as the etiologic basis of Lynch syndrome, there has been tremendous progress in the understanding of the spectrum of cancer risk associated with Lynch syndrome as well as in cancer prevention and risk-reduction strategies. The past few years, in particular, have brought transformative changes in the treatment of Lynch syndrome-associated cancers with immune checkpoint inhibitors. In parallel, advances in next-generation sequencing (NGS) technologies now allow rapid and scalable somatic and germline sequencing that promises to help identify Lynch syndrome in individuals who otherwise lack classic phenotypes. Last, real progress is being made to understand more sophisticated methods of precision cancer prevention, including chemotherapeutic prevention agents (e.g., aspirin) and strategies that leverage the immune system to facilitate primary cancer prevention in otherwise-healthy Lynch syndrome carriers.

Mismatch repair deficiency assessment by immunohistochemistry: for Lynch syndrome screening and beyond

While mismatch repair (MMR) deficiency has been studied extensively, the assessment of MMR status in colorectal and other cancers remains highly relevant, particularly in light of recent data demonstrating that MMR deficiency is a strong predictor for treatment benefit with immune checkpoint inhibitors across multiple tumor types. In colorectal cancer, there is a growing consensus in support of routine MMR testing for Lynch syndrome screening, to inform prognosis and adjuvant chemotherapy use in early stage disease, and to predict response to immunotherapy in advanced disease. Here, we provide a review of the Ventana MMR Immunohistochemistry Panel, which was recently approved by the US FDA for use in Lynch syndrome screening.

A framework to build capacity for a reflex-testing program for Lynch syndrome

PURPOSE

Lynch syndrome (LS) is the most common inherited cause of colorectal cancer. Although testing all colorectal tumors for LS is recommended, the uptake of reflex-testing programs within health systems has been limited. This multipronged study describes the design of a provincial program for reflex testing in Ontario, Canada.

METHODS

We recruited key stakeholders to participate in qualitative interviews to explore the barriers and facilitators to the implementation of a reflex-testing program. Data were analyzed in an iterative manner, key themes identified, and a framework for a proposed program developed.

RESULTS

Twenty-six key informants participated in our interviews, and several themes were identified. These included providing education for stakeholders (patients, primary care providers, surgeons); challenges with sustaining various resources (laboratory costs, increased workload for pathologists); ensuring consistency of reporting test results; and developing a plan to measure program success. Using these themes, a framework for the reflex-testing program was developed. At a subsequent stakeholder meeting, the framework was refined, and recommendations were identified.

CONCLUSIONS

This study identifies factors to ensure the effective implementation of a population-level program for reflex LS testing. The final product is a prototype that can be utilized in other jurisdictions, taking into account local environmental considerations.

Barriers to Lynch Syndrome Testing and Preoperative Result Availability in Early-onset Colorectal Cancer: A National Physician Survey Study

Objective

Although widely recommended, Lynch syndrome (LS) testing with tumor microsatellite instability (MSI) and/or immunohistochemistry (IHC) is infrequently performed in early-onset colorectal cancer (CRC), and CRC generally. Reasons are poorly understood. Hence, we conducted a national survey focusing on gastroenterologists, as they are frequently first to diagnose CRC, assessing testing barriers and which specialist is felt responsible for ordering MSI/IHC. Additionally, we assessed factors influencing timing of MSI/IHC ordering; testing on colonoscopy biopsy, opposed to post-operative surgical specimens, assists decisions on preoperative germline genetic testing and extent of colonic resection (ECR).

Methods

A 21-question web-based survey was distributed through an American College of Gastroenterology email listing.

Results

In total 509 completed the survey. 442 confirmed gastroenterologists were analyzed. Only 33.4% felt gastroenterologists were responsible for MSI/IHC ordering; pathologists were believed most responsible (38.6%). Cost, unfamiliarity interpreting results and unavailable genetic counseling most commonly prevented routine ordering (33.3%, 29.2%, 24.9%, respectively). In multivariable analysis, non-academic and rural settings were associated with cost and genetic counseling barriers. Only 46.1% felt MSI/IHC should always be performed on colonoscopy biopsy. Guideline familiarity predicted whether respondents felt surgical resection should be delayed until results returned given potential effect on ECR decisions.

Conclusion

Inconsistencies in who is felt should order MSI/IHC may lead to diffusion of responsibility, preventing consistent testing, including preoperatively. Assuring institutional universal testing protocols are in place, with focus on timing of testing, can optimize care. Strategies addressing cost barriers and genomic service availability in rural and non-academic settings can enhance testing. Greater emphasis on guideline familiarity is required.

Phosphorylation meets DNA mismatch repair

DNA mismatch repair (MMR) is a highly conserved process and ensures the removal of mispaired DNA bases and insertion-deletion loops right after replication. For this, a MutSα or MutSβ protein complex recognizes the DNA damage, MutLα nicks the erroneous strand, exonuclease 1 removes the wrong nucleotides, DNA polymerase δ refills the gap and DNA ligase I joins the fragments to seal the nicks and complete the repair process. The failure to accomplish these functions is associated with higher mutation rates and may lead to cancer, which highlights the importance of MMR by the maintenance of genomic stability. The post-replicative MMR implies that involved proteins are regulated at several levels, including posttranslational modifications (PTMs). Phosphorylation is one of the most common and major PTMs. Suitable with its regulatory force phosphorylation was shown to influence MMR factors thereby adjusting eukaryotic MMR activity. In this review, we summarized the current knowledge of the role of phosphorylation of MMR process involved proteins and their functional relevance.