Real-world study on microsatellite instability and mismatch repair deficiency testing patterns among patients with metastatic colorectal cancer in Spain.

PURPOSE: Clinical practice guidelines recommend that all patients with metastatic colorectal cancer (mCRC) should be tested for mismatch repair deficiency (dMMR) or microsatellite instability-high (MSI-H). We aimed to describe the dMMR/MSI-H testing practice in patients with mCRC in Spanish centers. METHODS: Multicenter, observational retrospective study that included patients newly diagnosed with mCRC or who progressed to a metastatic stage from early/localized stages. RESULTS: Three hundred patients were included in the study from May 2020 through May 2021, with a median age of 68 years, and two hundred twenty-five (75%) had stage IV disease at initial diagnosis; two hundred eighty-four patients received first-line treatment, and dMMR/MSI-H testing was performed in two hundred fifty-one (84%) patients. The results of the dMMR/MSI-H tests were available in 61 (24%) of 251 patients before the diagnosis of metastatic disease and in 191 (81%) of 236 evaluable patients for this outcome before the initiation of first-line treatment. Among the 244 patients who were tested for dMMR/MSI-H with IHC or PCR, 14 (6%) were MMR deficient. The most frequent type of first-line treatment was the combination of chemotherapy and biological agent, that was received by 71% and 50% of patients with MMR proficient and deficient tumors, respectively, followed by chemotherapy alone, received in over 20% of patients in each subgroup. Only 29% of dMMR/MSI-H tumors received first-line immunotherapy. CONCLUSION: Our study suggests that a high proportion of patients with mCRC are currently tested for dMMR/MSI-H in tertiary hospitals across Spain. However, there is still room for improvement until universal testing is achieved. TRIAL REGISTRATION: Not applicable.

PREMM5 distinguishes sporadic from Lynch syndrome-associated MMR-deficient/MSI-high colorectal cancer.

Current algorithms for diagnosing Lynch syndrome (LS) include multistep molecular tumor tests to distinguish LS-associated from sporadic colorectal cancer (CRC), which add cost and complexity to the evaluation. We hypothesized that PREMM5, a clinical LS prediction tool, could be an alternative approach to screen for LS, thereby lessening the need for specialized molecular diagnostics. We reviewed a consecutively ascertained institutional cohort of 1058 CRC patients on whom pathologic and clinical data were available, including prior LS germline testing. Data from MMR-D/MSI-H CRC patients were reviewed and PREMM5 scores were calculated for each individual. Using a PREMM5 score cutoff ≥ 2.5% to characterize the need for germline testing, we determined the rate of pathogenic/likely pathogenic germline variants (PGVs) in LS genes in patients with PREMM5 scores ≥ 2.5% versus < 2.5%. Sensitivity and negative predictive values (NPV) of PREMM5 were calculated for all MMR-D/MSI-H CRC patients, and those with MLH1-deficient CRC. MMR IHC and/or MSI results were available on 572/1058 cases. We identified 74/572 (12.9%) cases as MMR-D/MSI-H, of which 28/74 (37.8%) harbored a LS PGV. 11/49 (22.4%) patients with MLH1-deficient CRC harbored a LS PGV. PREMM5 had 100% sensitivity (95% CI: 87.7-100 for any MMR-D/MSI-H; 95% CI: 71.5-100 for MLH1-deficient CRC) and 100% NPV (95% CI: 83.2-100 for any MMR-D/MSI-H; 95% CI: 82.4-100 for MLH1-deficient CRC) for identifying LS PGVs in these cohorts. PREMM5 accurately distinguishes LS- from non-LS-associated MMR-D/MSI-H CRC without additional somatic molecular testing. These findings are particularly relevant for limited-resource settings where advanced molecular diagnostics may be unavailable.

Amplicon-based NGS test for assessing MLH1 promoter methylation and its correlation with BRAF mutation in colorectal cancer patients.

Detecting MLH1 promoter methylation is highly relevant to differentiate between possible Lynch syndrome patients or patients with sporadic causes of MLH1/PMS2 deficiency in colorectal (CRC) and endometrial cancers. Here, we aimed to develop a test for assessing MLH1 promoter methylation based in next generation sequencing (NGS), and to evaluate the concordance of MLH1 methylation and BRAF-V600 mutation status in CRC. For that, we performed a series of experiments with DNA from tumor, saliva and commercial control samples and our in house developed amplicon-based NGS test. In patients' samples, MLH1 methylation above 10% was only observed in tumors with MLH1/PMS2 loss. We confirmed the reproducibility and accuracy of MLH1 promoter analysis performing a serial dilution experiment with completely methylated and unmethylated control DNAs and a comparison between two NGS platforms (Ion Proton and Illumina). In MLH1/PMS2 deficient tumors, the MLH1 methylation status was concordant with the BRAF mutation status in 90% (18/20) of the cases. Our amplicon-based NGS test showed a great sensitivity and specificity for detecting MLH1 methylation in CRC samples, with a high agreement with the evaluation of BRAF mutation. This simple and affordable test could be used as a reflex test to identify patients with sporadic causes of MLH1/PMS2 deficiency in CRC, aiding to genetic test referral and identification of Lynch syndrome patients.

An effective algorithm to detect the possibility of being MSI phenotype in endometrial cancer given the BMI status and histological subtype: a statistical study.

PURPOSE: In endometrial cancer, the incidence of mutations in mismatch repair genes (MMR) is estimated at 17-30%. Patients with alterations at this level (MSI) are known to have different clinical and anatomopathological characteristics than those without this genetic alteration (MSS). In this study, we aim to identify the MSI phenotype in patients who underwent hysterectomy for endometrial cancer. We assessed the correlation of this phenotype with anatomoclinical parameters such as obesity and histological subtype. METHODS/PATIENTS: Clinical and anatomopathological data were collected from 147 patients diagnosed with endometrial cancer and an immunohistochemical study of MMR system proteins was performed. PMS2 and MSH6 proteins were evaluated as primary screening and subsequent evaluation of MLH1 and MSH6, respectively, if the former were negative. Statistical association between the anatomopathological data and the immunohistochemical result was analyzed. RESULTS AND CONCLUSIONS: 22.4% of our patients were MSI phenotype. We obtained statistically significant differences by multivariate analysis between endometrioid subtype and higher FIGO classification grade with MSI phenotype and obesity with MSS phenotype. Given these statistical results, we propose a function for predicting the probability of being MSI phenotype taking into account the histological subtype (endometrioid/non-endometrioid carcinoma) and FIGO grade as well as obesity. This prediction may be useful prior to hysterectomy, for genetic study of the MLH1 promoter and subsequent genetic counseling.

DNA Mismatch Repair-Deficient Colorectal Carcinoma: Referral Rate for Genetic Cancer Risk Assessment in a Brazilian Cancer Center.

BACKGROUND: Approximately 15% of colorectal cancers (CRCs) are deficient in DNA mismatch repair proteins (dMMR), a characteristic that can occur in both sporadic and hereditary CRC. Due to sparse studies on dMMR CRC in the Brazilian population, we conducted a retrospective analysis of referral rates for Genetic Cancer Risk Assessment of this population and also describing clinical and molecular characterization of these tumors. METHODS: A retrospective, longitudinal, and unicenter study that included patients with dMMR CRC detected by IHC analysis from Pathology Database of our institution, from January 2015 to July 2017. RESULTS: MMR IHC testing was performed in 998 CRC tumors, and 78 tumors (7.8%) had dMMR. The mean age at diagnosis was 56.8 years (17-90), and most patients were female (41 out of 78, 52.6%). Of the 52 patients with right-sided CRC, 40 tumors (77%) had loss of the MLH1 and/or PMS2 expression, and 12 tumors (23%) had loss of MSH2 and/or MSH6 expression (p = 0.005). From 78 patients with dMMR CRC, only 43 patients (55.1%) were referred for genetic counseling (GC), and of them, only 33 patients (76.7%) really went to GC consultation. A total of 21 patients with dMMR CRC performed genetic testing. CONCLUSION: Overall, genetic referral was less than expected in our population. Most of dMMR CRC patients did not receive GC, even in a cancer center, either due to the absence of referral or personal decision and few patients who pursued genetic counseling performed genetic testing.

Clinical and Molecular Assessment of Patients with Lynch Syndrome and Sarcomas Underpinning the Association with MSH2 Germline Pathogenic Variants.

Lynch syndrome (LS) is a hereditary cancer-predisposing syndrome associated most frequently with epithelial tumors, particularly colorectal (CRC) and endometrial carcinomas (EC). The aim of this study was to investigate the relationship between sarcomas and LS by performing clinical and molecular characterization of patients presenting co-occurrence of sarcomas and tumors from the LS spectrum. We identified 27 patients diagnosed with CRC, EC, and other LS-associated tumors who had sarcomas in the same individuals or families. Germline genetic testing, mismatch repair (MMR) protein immunohistochemistry, microsatellite instability (MSI), and other molecular analyses were performed. Five LS patients presenting personal or family history of sarcomas were identified (3 MSH2 carriers and 2 MLH1), with 2 having Muir-Torre phenotypes. For two MSH2 carriers we confirmed the etiology of the sarcomas (one liposarcoma and two osteosarcomas) as LS-related, since the tumors were MSH2/MSH6-deficient, MSI-high, or presented a truncated MSH2 transcript. Additionally, we reviewed 43 previous reports of sarcomas in patients with LS, which revealed a high frequency (58%) of MSH2 alterations. In summary, sarcomas represent a rare clinical manifestation in patients with LS, especially in MSH2 carriers, and the analysis of tumor biological characteristics can be useful for definition of tumor etiology and novel therapeutic options.

Simultaneous colonic adenocarcinoma and medulloblastoma in a 12-year-old with biallelic deletions in PMS2.

We describe a 12-year-old girl, simultaneously presenting with colonic adenocarcinoma and medulloblastoma from bialleic deletions in the mismatch repair gene PMS2. Her distinctive physical and clinical findings are characteristic of constitutional mismatch repair deficiency syndrome. Earlier recognition of such findings may permit better screening and more effective treatment.