Hereditary Cancer Syndrome — Inherited Risk Variants

A hereditary cancer syndrome is characterized by the presence of a germline pathogenic variant (mutation) passed down from a parent to their offspring. Unlike somatic mutations, which arise spontaneously in individual body tissues during life, germline variants are present in every nucleated cell from conception and can be transmitted to future generations with an autosomal dominant or recessive inheritance pattern.

These inherited alterations most commonly disrupt tumour suppressor genes or DNA mismatch repair genes, such as BRCA1, BRCA2, MLH1, or TP53. Because one functional copy of the gene is already defective at birth, cells require fewer subsequent somatic mutations to undergo malignant transformation, leading to earlier cancer onset and a propensity for multifocal or bilateral tumours.

Identifying a hereditary cancer syndrome transforms clinical care for both the patient and their biological relatives. For an individual diagnosed with cancer, genetic results can influence surgical decisions—such as choosing a bilateral mastectomy over a lumpectomy—and direct systemic therapy choices. For unaffected family members, genetic discovery allows predictive testing, empowering them to begin high-risk screening earlier, consider preventive risk-reducing medications or surgeries, and substantially lower cancer mortality.

Diagnosis relies on germline genetic testing, which is performed on DNA extracted from a simple blood draw or saliva sample rather than tumour tissue. Clinicians often use multi-gene next-generation sequencing (NGS) panels to examine dozens of cancer-susceptibility genes simultaneously. Pre-test and post-test genetic counselling is an essential component, helping patients interpret the personal, psychological, and familial implications of the results.

Hereditary cancer syndromes are linked to diverse malignancies. Hereditary Breast and Ovarian Cancer syndrome (HBOC), driven by BRCA1 and BRCA2, predisposes individuals to breast, ovarian, prostate, and pancreatic cancers. Lynch syndrome is tied to colorectal, endometrial, ovarian, and stomach cancers. Other conditions include Li-Fraumeni syndrome (sarcomas, brain tumours, leukemias) and Multiple Endocrine Neoplasia (endocrine tumours).

Finding an inherited variant informs precision treatment. Patients with BRCA-associated cancers frequently benefit from poly (ADP-ribose) polymerase (PARP) inhibitors or platinum-based chemotherapy because their tumours have defective homologous recombination repair. Cancers arising from Lynch syndrome frequently exhibit high microsatellite instability (MSI-H), rendering them exceptionally responsive to immune checkpoint inhibitors. Surgical management may also encompass prophylactic removal of unaffected at-risk organs.