A case of early onset rectal cancer of Lynch syndrome with a novel deleterious PMS2 mutation

Advances in Identification of Susceptibility Gene Defects of Hereditary Colorectal Cancer

Colorectal cancer (CRC) is a common malignant tumor of the digestive system worldwide, associated with hereditary genetic features. CRC with a Mendelian genetic predisposition accounts for approximately 5-10% of total CRC cases, mainly caused by a single germline mutation of a CRC susceptibility gene. The main subtypes of hereditary CRC are hereditary non-polyposis colorectal cancer (HNPCC) and familial adenomatous polyposis (FAP). With the rapid development of genetic testing methods, especially next-generation sequencing technology, multiple genes have now been confirmed to be pathogenic, including DNA repair or DNA mismatch repair genes such as APC, MLH1, and MSH2. Since familial CRC patients have poor clinical outcomes, timely clinical diagnosis and mutation screening of susceptibility genes will aid clinicians in establishing appropriate risk assessment and treatment interventions at a personal level. Here, we systematically summarize the susceptibility genes identified to date and the potential pathogenic mechanism of HNPCC and FAP development. Moreover, clinical recommendations for susceptibility gene screening, diagnosis, and treatment of HNPCC and FAP are discussed.

Feasibility of Segmental Colectomy Followed by Endoscopic Surveillance as a Treatment Strategy for Colorectal Cancer Patients with Lynch Syndrome

BACKGROUND

Initial surgical procedures for colorectal cancer (CRC) patients with Lynch syndrome remain controversial. This study assessed the validity of segmental colectomy (SGC) followed by endoscopic surveillance as a treatment strategy for CRC patients with Lynch syndrome.

METHODS

Among consecutive patients who underwent surgery for primary CRC between April 1985 and December 2014, 49 patients were observed to have germline mutations in a mismatch repair gene, and 38 patients who underwent SGC followed by periodic endoscopic surveillance at our institution were evaluated for metachronous CRC, need for secondary surgery, and the details of endoscopic surveillance.

RESULTS

Of the 38 patients who underwent SGC followed by periodic endoscopic surveillance at our institution, 6 (15.8%) patients showed metachronous CRC, 3 (7.9%) patients underwent endoscopic resection, and the other 3 patients (7.9%) underwent secondary surgery. The dispersion of the endoscopic surveillance interval was significantly greater in patients with metachronous CRC (364 ± 332.9 days) than in those without metachronous CRC (370 ± 129.7 days; p < 0.001).

CONCLUSIONS

SGC followed by annual endoscopic surveillance was feasible as a treatment strategy for CRC patients with Lynch syndrome, because the incidence of metachronous CRC and the need for secondary surgery were low. Annual and periodic endoscopic surveillance might be essential for early detection of metachronous CRC and prevention of secondary surgery because of metachronous CRC in CRC patients with Lynch syndrome after SGC.

Germline PMS2 mutation screened by mismatch repair protein immunohistochemistry of colorectal cancer in Japan

Germline PMS2 gene mutations were detected by RT‐PCR/direct sequencing of total RNA extracted from puromycin‐treated peripheral blood lymphocytes (PBL) and multiplex ligation‐dependent probe amplification (MLPA) analyses of Japanese patients with colorectal cancer (CRC) fulfilling either the revised Bethesda Guidelines or being an age at disease onset of younger than 70 years, and screened by mismatch repair protein immunohistochemistry of formalin‐fixed paraffin embedded sections. Of the 501 subjects examined, 7 (1.40%) showed the downregulated expression of the PMS2 protein alone and were referred to the genetic counseling clinic. Germline PMS2 mutations were detected in 6 (85.7%), including 3 nonsense and 1 frameshift mutations by RT‐PCR/direct sequencing and 2 genomic deletions by MLPA. No mutations were identified in the other MMR genes (i.e. MSH2,MLH1 and MSH6). The prevalence of the downregulated expression of the PMS2 protein alone was 1.40% among the subjects examined and IHC results predicted the presence of PMS2 germline mutations. RT‐PCR from puromycin‐treated PBL and MLPA may be employed as the first screening step to detect PMS2 mutations without pseudogene interference, followed by the long‐range PCR/nested PCR validation using genomic DNA.