Biology
Genetic Testing for Hereditary Cancer Syndromes
Quick fact
Mutations in the BRCA1 and BRCA2 genes can increase a woman's lifetime risk of breast cancer up to 72% and ovarian cancer up to 44%, compared to about 12% and 1.3% in the general population.
Why this is interesting
Have you ever wondered why some families seem to have many members affected by cancer? Genetic testing can uncover the hidden hereditary links that explain such patterns.
Read the full explanation
Understanding Genetic Testing for Hereditary Cancer Syndromes
Most cancers are sporadic, caused by mutations that accumulate over a lifetime. However, about 5-10% of cancers are hereditary, caused by a single mutated gene passed down from a parent. These mutations are present in every cell of the body from birth. Genetic testing for hereditary cancer syndromes analyzes specific genes, like BRCA1 and BRCA2, to find such inherited mutations. The process starts with a blood or saliva sample. If a mutation is found, it explains why cancer clusters in the family and allows other family members to be tested for the same mutation. This testing is not a routine screening tool; it is recommended when there is a personal or family history suggesting a hereditary syndrome, such as several relatives with the same type of cancer, early-onset cancer, or rare cancers like ovarian or male breast cancer. Genetic counseling before testing helps individuals understand the potential risks, benefits, and limitations of the test.
A deeper explanation
The underlying principle is that specific genes encode proteins that protect against cancer, such as tumor suppressors that repair DNA damage or regulate cell growth. A germline mutation in one copy of such a gene predisposes the person to cancer because it follows an autosomal dominant inheritance pattern: inheriting one mutated allele increases the risk, though cancer usually requires a second somatic hit in the other allele (the 'two-hit hypothesis'). BRCA1 and BRCA2 are key examples; they are involved in repairing double-strand DNA breaks. When these genes are faulty, DNA damage accumulates, leading to mutations that drive cancer. Testing uses next-generation sequencing to read the entire coding sequence of many cancer-risk genes simultaneously. Results can be positive (mutation found), negative, or a variant of uncertain significance (VUS), where the health impact is unknown. A positive result empowers individuals to take preventive measures, such as increased surveillance with MRI or colonoscopy, or risk-reducing surgeries like prophylactic mastectomy. This proactive approach has been shown to reduce cancer incidence and mortality in high-risk families.