Development of an MSI-positive colon tumor with aberrant DNA methylation in a PPAP patient

Deficient Mismatch Repair and Microsatellite Instability in Solid Tumors

The integrity of the genome is maintained by mismatch repair (MMR) proteins that recognize and repair base mismatches and insertion/deletion errors generated during DNA replication and recombination. A defective MMR system results in genome-wide instability and the progressive accumulation of mutations. Tumors exhibiting deficient MMR (dMMR) and/or high levels of microsatellite instability (termed "microsatellite instability high", or MSI-H) have been shown to possess fundamental differences in clinical, pathological, and molecular characteristics, distinguishing them from their "microsatellite stable" (MSS) counterparts. Molecularly, they are defined by a high mutational burden, genetic instability, and a distinctive immune profile. Their distinct genetic and immunological profiles have made dMMR/MSI-H tumors particularly amenable to treatment with immune checkpoint inhibitors (ICIs). The ongoing development of biomarker-driven therapies and the evaluation of novel combinations of immune-based therapies, with or without the use of conventional cytotoxic treatment regimens, continue to refine treatment strategies with the goals of maximizing therapeutic efficacy and survival outcomes in this distinct patient population. Moreover, the resultant knowledge of the mechanisms by which these features are suspected to render these tumors more responsive, overall, to immunotherapy may provide information regarding the potential optimization of this therapeutic approach in tumors with proficient MMR (pMMR)/MSS tumors.

Case Report: A case of synchronous multiple early gastric cancer with a microsatellite instability-high phenotype

Synchronous multiple early gastric cancer (SMEGC) is a relatively uncommon variant of early gastric cancer (EGC). In this report, we present a case of SMEGC accompanied by a microsatellite instability-high (MSI-H) phenotype. The patient was a 69-year-old man who presented to our hospital with abdominal pain. The endoscopic examination revealed two lesions. Both lesions were pathologically confirmed as EGC, then the patient subsequently underwent endoscopic submucosal dissection (ESD). Nine months post-procedure, the patient returned with recurrent abdominal pain, leading to the diagnosis of a new EGC. Immunohistochemical analysis demonstrated that all lesions exhibited an MSI-H phenotype and BRAF mutant expression, suggesting that these lesions are not associated with Lynch syndrome-related EGC. The case was ultimately diagnosed as SMEGC with an MSI-H phenotype. The current evidence and clinical experience suggest that patients with advanced MSI-H are likely to benefit from immunotherapy and should be considered for early systemic treatment with immunotherapy as a central component. At present, research studies on the molecular characteristics of SMEGC are limited, underscoring the importance of conducting comprehensive molecular diagnostics of each EGC patient, which could help clinicians thoroughly understand the lesion's characteristics.

Multiple duodenal epithelial tumors in a patient with polymerase proofreading-associated polyposis in POLE variant

Polymerase proofreading-associated polyposis (PPAP) is a rare disease with autosomal-dominant inheritance caused by germline variants in the POLE and POLD1 genes. PPAP has been reported to increase the risk of multiple cancers, including colon, duodenal, and endometrial cancers. Herein, we report a case in which multiple duodenal tumors led to the detection of a POLE mutation. A 43-year-old woman underwent esophagogastroduodenoscopy (EGD). Multiple duodenal tumors were detected, and all lesions were treated endoscopically. The patient had a history of multiple colorectal cancers and endometrial cancer along with a family history of cancer; hence, genetic testing was performed, and POLE variant, c.1270C > G (p.Leu424Val) was detected. Hereditary colorectal cancer syndromes should be considered in patients with colorectal cancer who have multiple cancers or a family history of cancer, and multigene panel sequencing is useful in confirming the diagnosis. In addition, duodenal tumors frequently coexist in patients with PPAP-carrying POLE variants, while the endoscopic treatment for duodenal tumors becomes safe and useful with several new approaches. Therefore, surveillance EGD is necessary in such patients for the early detection and treatment of duodenal tumors.

Unraveling the impact of a germline heterozygous POLD1 frameshift variant in serrated polyposis syndrome

Serrated polyposis syndrome (SPS) is one of the most frequent polyposis syndromes characterized by an increased risk for developing colorectal cancer (CRC). Although SPS etiology has been mainly associated with environmental factors, germline predisposition to SPS could also be relevant for cases with familial aggregation or a family history of SPS/CRC. After whole-exome sequencing of 39 SPS patients from 16 families, we identified a heterozygous germline frameshift variant in the POLD1 gene (c.1941delG, p.(Lys648fs*46)) in a patient with SPS and CRC. Tumor presented an ultra-hypermutated phenotype and microsatellite instability. The POLD1 germline variant segregated in three additional SPS-affected family members. We attempted to create yeast and cellular models for this variant but were no viable. Alternatively, we generated patient-derived organoids (PDOs) from healthy rectal tissue of the index case, as well as from a control donor. Then, we challenged PDOs with a DNA-damaging agent to induce replication stress. No significant differences were observed in the DNA damage response between control and POLD1-Lys648fs PDOs, nor specific mutational signatures were observed. Our results do not support the pathogenicity of the analyzed POLD1 frameshift variant. One possible explanation is that haplosufficiency of the wild-type allele may be compensating for the absence of expression of the frameshift allele. Overall, future work is required to elucidate if functional consequences could be derived from POLD1 alterations different from missense variants in their proofreading domain. To our knowledge, our study presents the first organoid model for germline POLD1 variants and establishes the basis for its use as a model for disease in SPS, CRC and other malignancies.

How many is too many? Polyposis syndromes and what to do next

PURPOSE OF REVIEW

The goal of this review is to help providers recognize, diagnose and manage gastrointestinal (GI) polyposis syndromes.

RECENT FINDINGS

Intestinal polyps include a number of histological sub-types such as adenomas, serrated, hamartomas among others. Over a quarter of individuals undergoing screening colonoscopy are expected to have colonic adenomas. Although it is not uncommon for adults to have a few GI polyps in their lifetime, some individuals are found to have multiple polyps of varying histology throughout the GI tract. In these individuals, depending on polyp histology, number, location and size as well as extra-intestinal features and/or family history, a polyposis syndrome should be considered with appropriate testing and management.

SUMMARY

Diagnosis and management of polyposis syndromes has evolved with advent of multigene panel testing and new data on optimal surveillance strategies. Evidence-based recommendations and current practice guidelines for polyposis syndromes are reviewed here. Areas of uncertainty and future research are also highlighted.

Prevalence of Lynch syndrome in women with mismatch repair-deficient ovarian cancer

BACKGROUND

There are limited data on the prevalence of Lynch syndrome (LS) in women with primary ovarian cancer with mismatch repair deficiency (MMR-D) by immunohistochemistry (IHC).

MATERIALS AND METHODS

Three hundred and eight cases of primary ovarian, fallopian, and peritoneal cancer between January 2012 and December 2019 were evaluated for MMR-D by IHC. The incidence of LS in this cohort was evaluated.

RESULTS

MMR-D by IHC was identified in 16 of 308 (5.2%) (95% CI: 3.2%-8.3%) primary ovarian-related cancers. Most cases with MMR-D were endometrioid (n = 11, 68.7%); (95% CI: 44.2%-86.1%). MSH2/MSH6 protein loss was detected in eight cases (50.0%); (95% CI: 28.0%-72.0%) and MLH1/PMS2 protein loss was detected in four cases (25.0%); (95% CI: 9.7%-50.0%). MSH6 protein loss was detected in two cases (12.5%); (95% CI: 2.2%-37.3%) and PMS2 protein loss was detected in two cases (12.5%); (95% CI: 2.2%-37.3%). All four cases with MLH1/PMS2 protein loss had MLH1 promotor hypermethylation. All 12 women with ovarian cancer suggestive of LS underwent germline testing and 8 (66.6%); (95% CI: 38.8%-86.5%) were confirmed to have LS.

CONCLUSIONS

Most ovarian cancers with somatic MMR-D were confirmed to have LS in this cohort. Germline testing for LS in addition to BRCA1/2 for all women with an epithelial ovarian cancer would be efficient and would approach 100% sensitivity for identifying Lynch syndrome. Utilization of a multigene panel should also be considered, given the additional non-Lynch germline mutation identified in this cohort.

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.

The first case report of polymerase proofreading-associated polyposis in POLD1 variant, c.1433G>A p.S478N, in Japan

Polymerase proofreading-associated polyposis, caused by germline variants in the exonuclease domains of POLD1 and POLE, is a dominantly inherited rare condition characterized by oligo-adenomatous polyposis and increased risk of colorectal cancer, endometrial cancer and brain tumours. We report the first Japanese case of polymerase proofreading-associated polyposis carrying a POLD1 variant. The proband was a Japanese woman who had undergone resections of early colorectal carcinomas repeatedly and a hysterectomy with bilateral oophorectomy for endometrial cancer, all of which were diagnosed within 2 years after the first colectomy at 49 year old. Colonoscopic examinations demonstrated at least 14 non-cancerous polypoid lesions, some of which were histologically confirmed to be adenoma. Multigene panel sequencing identified a missense variant in POLD1 (c.1433G>A). Although her relatives did not undergo genetic testing, her father and paternal grandfather died of brain tumours at 53 and ~30 years of age, respectively.