Lynch syndrome

Lynch syndrome
Name	Lynch syndrome
Synonyms	Hereditary nonpolyposis colorectal cancer
Field	Medical genetics, Oncology, Gastroenterology

Lynch syndrome Lynch syndrome is an inherited cancer predisposition syndrome characterized by pathogenic variants in DNA mismatch repair genes that markedly increase lifetime risk of colorectal and several extracolonic malignancies. It is a major focus of medical genetics, oncology, and gastroenterology because early identification enables targeted surveillance, preventive surgery, and cascade testing of relatives. Clinical management intersects with guidelines from organizations such as the National Comprehensive Cancer Network, United States Preventive Services Task Force, and international hereditary cancer consortia.

Introduction

Lynch syndrome results from germline mutations in mismatch repair genes and is historically termed hereditary nonpolyposis colorectal cancer; it was first recognized through family-based observations that linked early-onset colorectal carcinoma to recurrent patterns of extracolonic tumors in pedigrees reported by investigators associated with institutions like Johns Hopkins Hospital and Mayo Clinic. The syndrome has implications for specialties including pathology, genetic counseling, surgical oncology, and public health programs administered by entities such as the Centers for Disease Control and Prevention.

Genetics and Pathophysiology

Pathogenic germline variants most commonly affect the MMR genes MLH1, MSH2, MSH6, and PMS2, and less frequently involve deletions of the 3' end of EPCAM leading to epigenetic silencing of MSH2. Loss of MMR function produces high levels of microsatellite instability and an elevated tumor mutation burden, a molecular phenotype extensively characterized in studies from laboratories at institutions like Dana–Farber Cancer Institute and Memorial Sloan Kettering Cancer Center. The somatic second-hit events follow Knudson's two-hit model originally articulated in work connected to researchers at Cold Spring Harbor Laboratory, and the ensuing genomic instability drives oncogenesis across multiple tissues. Tumors arising in MMR-deficient backgrounds often show distinct histopathologic features described in publications from The Royal College of Pathologists and are predictive of response to immune checkpoint blockade agents developed by companies such as Merck & Co. and Bristol Myers Squibb.

Clinical Presentation and Associated Cancers

Affected individuals commonly present with early-onset colorectal cancer and synchronous or metachronous lesions; influential case series from centers like Cleveland Clinic document variable age of onset by gene, with MLH1 and MSH2 carriers typically showing earlier presentation than MSH6 or PMS2 carriers. Extracolonic cancers include endometrial carcinoma, ovarian carcinoma, gastric carcinoma, small bowel adenocarcinoma, hepatobiliary cancers, urothelial carcinoma of the upper tract, and certain sebaceous neoplasms as in Muir–Torre syndrome. Gynecologic oncology literature from institutions such as University College London and Massachusetts General Hospital emphasizes endometrial screening in women. Reports from oncology groups like European Society for Medical Oncology detail associations with pancreatic and brain tumors in selected pedigrees.

Diagnosis and Screening

Universal tumor screening protocols recommend immunohistochemistry for MMR proteins and microsatellite instability testing for colorectal and endometrial cancers, practices promoted by bodies including the American Society of Clinical Oncology and the College of American Pathologists. Positive tumor screening prompts germline testing using sequencing and deletion/duplication analysis, often performed at commercial laboratories such as Invitae and academic centers like Stanford University School of Medicine. Clinical criteria historically include the Amsterdam and revised Bethesda guidelines developed by collaborative working groups in Europe and North America, while modern algorithms incorporate multigene panel testing endorsed by organizations like the American College of Medical Genetics and Genomics.

Management and Surveillance

Risk-reduction strategies include intensified colonoscopic surveillance at intervals recommended by panels from the National Institute for Health and Care Excellence and prophylactic surgeries—such as risk-reducing hysterectomy with bilateral salpingo-oophorectomy—guided by gynecologic oncology consensus statements from societies including the Society of Gynecologic Oncology. Chemoprevention with agents assessed in randomized trials sponsored by groups like the United Kingdom Medical Research Council has been explored, and immunotherapy for MMR-deficient tumors is informed by pivotal trials reported by cooperative groups such as the National Cancer Institute-sponsored networks. Cascade testing programs coordinated through regional genetics services and patient advocacy organizations like Lynch Syndrome International facilitate identification of at-risk relatives.

Prognosis and Counseling

Prognosis varies by cancer type, stage at diagnosis, and specific gene mutated; survival outcomes for MMR-deficient colorectal cancers have been examined in population-based cohorts from registries such as the Surveillance, Epidemiology, and End Results Program and consortia like the Colon Cancer Family Registry. Genetic counseling integrates risk estimates from empirical studies at institutions including Kings College London and Harvard Medical School and addresses reproductive options such as preimplantation genetic testing, coordinated with fertility centers and regulatory frameworks in jurisdictions like United Kingdom and United States. Psychosocial support resources are offered through nonprofit organizations and hospital-based genetic services.

Epidemiology and History

Population-based estimates suggest a prevalence of pathogenic MMR variants of roughly 1 in 279 to 1 in 370 in some cohorts analyzed by researchers at public health agencies such as Public Health England and the Centers for Disease Control and Prevention, though ascertainment varies by ancestry and founder mutations identified in populations including Ashkenazi Jews and families from regions of Iceland and Finland. Historical milestones encompass early pedigree descriptions in the mid-20th century, the delineation of Amsterdam criteria by European researchers, and the molecular elucidation of MMR genes during the 1990s by teams at laboratories associated with University of Washington and Institut Pasteur.

Category:Genetic disorders