Recommendations on Surveillance and Management of Biallelic Mismatch Repair Deficiency (BMMRD) Syndrome: A Consensus Statement by the US Multi-society Task Force on Colorectal Cancer

Germline susceptibility from broad genomic profiling of pediatric brain cancers

Background

Identifying germline predisposition in CNS malignancies is of increasing clinical importance, as it contributes to diagnosis and prognosis, and determines aspects of treatment. The inclusion of germline testing has historically been limited due to challenges surrounding access to genetic counseling, complexity in acquiring a germline comparator specimen, concerns about the impact of findings, or cost considerations. These limitations were further defined by the breadth and scope of clinical testing to precisely identify complex variants as well as concerns regarding the clinical interpretation of variants including those of uncertain significance.

Methods

In the course of conducting an IRB-approved protocol that performed genomic, transcriptomic and methylation-based characterization of pediatric CNS malignancies, we cataloged germline predisposition to cancer based on paired exome capture sequencing, coupled with computational analyses to identify variants in known cancer predisposition genes and interpret them relative to established clinical guidelines.

Results

In certain cases, these findings refined diagnosis or prognosis or provided important information for treatment planning.

Conclusions

We outline our aggregate findings on cancer predisposition within this cohort which identified 16% of individuals (27 of 168) harboring a variant predicting cancer susceptibility and contextualize the impact of these results in terms of treatment-related aspects of precision oncology.

A Constitutional Mismatch Repair Deficiency Syndrome Presented With an Advanced Rectal Cancer in a Juvenile Female: A Case Report and Literature Review

The constitutional mismatch repair deficiency (CMMRD) syndrome is a rare and challenging condition with a poor prognosis. It results from biallelic mismatch repair gene mutations and leads to multiorgan cancers. Therefore, we report the first case of advanced juvenile rectal cancer related to CMMRD syndrome in the Gulf region. She is a 13-year-old female, born to non-consanguineous parents with a positive family history of malignancy, presented with an eight-month history of a retractable bulging anal mass associated with diarrhea mixed with blood and constitutional symptoms. She was cachectic with café au lait spots all over her body. Upon investigation, she was found to have invasive rectal adenocarcinoma. The case was started on neoadjuvant chemoradiotherapy in addition to genetic testing which showed a homozygous pathogenic variant in PMS2, indicating CMMRD syndrome. The patient underwent pre-operative post-neoadjuvant reassessment followed by laparoscopic total proctocolectomy with ileal J-pouch creation and ileoanal anastomosis with temporary diverting loop ileostomy which later on was reversed with no complications or recurrence. The family declined to continue the adjuvant therapy but accepted the surveillance programs and genetic testing. Unusual or late presentation secondary to a very rare syndrome like CMMRD is a major challenge to clinicians, hence a high index of suspicion and proper utilization of genetics programs might be the best available solutions.

Intensive surveillance endoscopy for multiple gastrointestinal tumors in a patient with constitutional mismatch repair deficiency: case report

BACKGROUND

Constitutional mismatch repair deficiency (CMMRD) is an extremely rare autosomal recessive hereditary disease characterized by the absence of mismatch repair gene activity from birth, which results in brain tumors, colonic polyposis, gastrointestinal cancers, and lymphomas later in life. An aggressive approach, including colectomy or proctocolectomy, is recommended for the treatment of colorectal cancer. Additionally, partial colectomy with subsequent endoscopic surveillance may be an alternative strategy due to poor patient's condition, although there is no evidence of surveillance endoscopy after partial colectomy for CMMRD.

CASE PRESENTATION

A 13-year-old male patient with a history of T-lymphoblastic lymphoma underwent total gastrointestinal endoscopy, which revealed rectal cancer, colorectal polyposis, and duodenal adenoma. Differential diagnosis included constitutional mismatch repair deficiency according to its scoring system and microsatellite instability, and subsequent germline mutation testing for mismatch repair genes confirmed the diagnosis of constitutional mismatch repair deficiency based on a homozygous mutation in mutS homolog 6 (MSH6). The patient and his family refused colectomy due to the high risk of malignancies other than colorectal cancer, which could require radical surgery. Therefore, the patient underwent low anterior resection of the rectosigmoid colon for rectal cancer and intensive surveillance endoscopy for the remaining colon polyposis. During the 3-year period after initial surgery, 130 polyps were removed and the number of polyps gradually decreased during 6-months interval surveillance endoscopies, although only one polyp was diagnosed as invasive adenocarcinoma (pT1).

CONCLUSIONS

Our experience of short surveillance endoscopy illustrates that this strategy might be one of options according to patient's condition.

Update on genetic predisposition to colorectal cancer and polyposis

The present article summarizes recent developments in the characterization of genetic predisposition to colorectal cancer (CRC). The main themes covered include new hereditary CRC and polyposis syndromes, non-CRC hereditary cancer genes found mutated in CRC patients, strategies used to identify novel causal genes, and review of candidate genes that have been proposed to predispose to CRC and/or colonic polyposis. We provide an overview of newly described genes and syndromes associated with predisposition to CRC and polyposis, including: polymerase proofreading-associated polyposis, NTHL1-associated polyposis, mismatch repair gene biallelic inactivation-related adenomatous polyposis (including MSH3- and MLH3-associated polyposes), GREM1-associated mixed polyposis, RNF43-associated serrated polyposis, and RPS20 mutations as a rare cause of hereditary nonpolyposis CRC. The implementation of next generation sequencing approaches for genetic testing has exposed the presence of pathogenic germline variants in genes associated with hereditary cancer syndromes not traditionally linked to CRC, which may have an impact on genetic testing, counseling and surveillance. The identification of new hereditary CRC and polyposis genes has not deemed an easy endeavor, even though known CRC-related genes explain a small proportion of the estimated familial risk. Whole-genome sequencing may offer a technology for increasing this proportion, particularly if applied on pedigree data allowing linkage type of analysis. The final section critically surveys the large number of candidate genes that have been recently proposed for CRC predisposition.

Constitutional mismatch repair deficiency as a differential diagnosis of neurofibromatosis type 1: consensus guidelines for testing a child without malignancy

Constitutional mismatch repair deficiency (CMMRD) is a rare childhood cancer predisposition syndrome caused by biallelic germline mutations in one of four mismatch-repair genes. Besides very high tumour risks, CMMRD phenotypes are often characterised by the presence of signs reminiscent of neurofibromatosis type 1 (NF1). Because NF1 signs may be present prior to tumour onset, CMMRD is a legitimate differential diagnosis in an otherwise healthy child suspected to have NF1/Legius syndrome without a detectable underlying NF1/SPRED1 germline mutation. However, no guidelines indicate when to counsel and test for CMMRD in this setting. Assuming that CMMRD is rare in these patients and that expected benefits of identifying CMMRD prior to tumour onset should outweigh potential harms associated with CMMRD counselling and testing in this setting, we aimed at elaborating a strategy to preselect, among children suspected to have NF1/Legius syndrome without a causative NF1/SPRED1 mutation and no overt malignancy, those children who have a higher probability of having CMMRD. At an interdisciplinary workshop, we discussed estimations of the frequency of CMMRD as a differential diagnosis of NF1 and potential benefits and harms of CMMRD counselling and testing in a healthy child with no malignancy. Preselection criteria and strategies for counselling and testing were developed and reviewed in two rounds of critical revisions. Existing diagnostic CMMRD criteria were adapted to serve as a guideline as to when to consider CMMRD as differential diagnosis of NF1/Legius syndrome. In addition, counselling and testing strategies are suggested to minimise potential harms.