BRCA1 and BRCA2 are genes that normally help maintain DNA integrity. Inherited harmful variants can increase breast cancer risk by weakening important cellular safeguards. Their discovery also helped explain how defects in DNA repair can create vulnerabilities that researchers may be able to target.
This distinction—between a normal gene and a harmful variant in that gene—is central to understanding hereditary cancer biology. NCI: BRCA Gene Changes
How researchers found BRCA1
For decades, researchers observed that breast cancer sometimes clustered strongly in families, especially when disease appeared at younger ages. The question was whether that pattern could be explained by inherited genetic susceptibility rather than shared environment alone.
In 1990, Mary-Claire King and colleagues reported linkage between early-onset familial breast cancer and a region on chromosome 17q21. The finding mapped a susceptibility locus; it did not yet identify the gene sequence. Hall et al. 1990
Four years later, a large collaborative effort identified BRCA1 by positional cloning. The discovery made it possible to move from a mapped susceptibility region to a defined gene whose variants could be studied directly. Miki et al., Science (1994)
How BRCA1 and BRCA2 support DNA repair
BRCA1 and BRCA2 participate in DNA-repair pathways that protect cells from accumulating dangerous genomic changes. One important role is in homologous recombination, a high-fidelity mechanism used to repair double-strand DNA breaks.
Everyone normally carries two copies of each gene. A person with an inherited harmful variant typically begins life with one altered copy and one functional copy. If the remaining functional copy is later lost or disrupted in a cell, that cell can become deficient in BRCA-dependent DNA repair. This “two-hit” logic helps connect inherited susceptibility to a cellular mechanism.
How harmful BRCA variants affect cancer risk
A harmful germline BRCA1 or BRCA2 variant substantially increases lifetime risk, but it does not make cancer inevitable. NCI currently estimates that more than 60% of women who inherit a harmful BRCA1 or BRCA2 change will develop breast cancer during their lifetime, compared with about 13% in the general female population. Risk estimates vary by gene, family, age, ancestry, and study population.
BRCA-related risk also extends beyond breast cancer, including ovarian and, in some settings, prostate and pancreatic cancers. That is why a germline result can carry implications for relatives as well as for the person tested.
Germline and somatic BRCA changes
A germline variant is present in egg or sperm cells and can be passed to offspring; many are inherited from a parent, although some arise newly. A somatic alteration is acquired in particular cells during a person’s lifetime. Finding a BRCA alteration in a tumor therefore does not by itself establish that it is inherited.
This distinction matters both scientifically and clinically. A tumor-specific change may help explain tumor biology, while a confirmed germline variant may also inform inherited risk for the individual and family members. NCI recommends discussing germline testing when tumor testing identifies a harmful BRCA change.
Why DNA repair defects led to PARP inhibitor research
A cancer cell with defective homologous recombination may become more dependent on alternative DNA-repair mechanisms. PARP inhibitors exploit part of this vulnerability by interfering with repair processes that BRCA-deficient cells may rely on to survive DNA damage.
The OlympiAD phase 3 trial provided clinical evidence for this principle in a defined population with germline BRCA-mutated, HER2-negative metastatic breast cancer. Olaparib improved progression-free survival compared with physician’s-choice chemotherapy in that trial. The result did not mean that every BRCA alteration predicts identical benefit; it demonstrated that a mechanistic vulnerability could be translated into a treatment strategy for a specific population. OlympiAD, New England Journal of Medicine (2017)
What a variant of uncertain significance means
Genetic tests sometimes identify a variant of uncertain significance, or VUS. A VUS is not the same as a known harmful variant. Its meaning may change as more evidence becomes available, and clinical decisions should not treat uncertainty as proof of inherited cancer risk.
BRCA1 and BRCA2 are also not the only genes associated with hereditary breast cancer. Modern genetic assessment may consider additional genes depending on personal and family history. The scientific lesson from BRCA is broader than two gene names: inherited cancer risk can arise from defects in biological systems that normally protect the genome.
From inherited risk to a research mechanism
The BRCA story connects family history, gene discovery, DNA-repair biology, and treatment research. Those connections are powerful, but a genetic result still needs careful interpretation. Decisions about breast cancer screening or treatment depend on the person’s clinical context, not on the gene name alone.
This article is intended for scientific education and does not provide individualized medical advice, diagnosis, or treatment recommendations.
Sources and further reading
- NCI — BRCA Gene Changes: Cancer Risk and Genetic Testing
- Hall et al. — Linkage of Early-Onset Familial Breast Cancer to Chromosome 17q21
- Miki et al. — A Strong Candidate for the Breast and Ovarian Cancer Susceptibility Gene BRCA1
- Robson et al. — Olaparib for Metastatic Breast Cancer in Patients with a Germline BRCA Mutation
