BRCA1 Gene and Cancer: What Patients Need to Know

BRCA1 (BReast CAncer gene 1) is a tumour suppressor gene that produces a protein involved in repairing DNA. Every day, cells experience DNA damage, including double-strand breaks, from normal metabolism, replication errors and environmental exposures. The BRCA1 protein is a key component of homologous recombination, a highly accurate repair pathway that uses a matching copy of DNA as a template to mend the break precisely. When BRCA1 is faulty, cells must fall back on less accurate repair mechanisms, and DNA damage accumulates over time. This genomic instability is what eventually allows a normal cell to become cancerous.

BRCA1 mutations fall into two distinct categories that are easy to confuse but mean very different things. A germline mutation is present from birth in every cell of the body, including eggs or sperm, so it can be passed to children and is shared with some blood relatives; germline testing typically uses a blood or saliva sample. A somatic mutation arises later, only within the cells of a specific tumour, as one of many DNA changes that accumulate during cancer development; it is found only through testing of tumour tissue and has no implication for family members. Roughly similar biomarker behaviour applies to the related gene BRCA2, and the two are often tested together as part of the same panel.

If you are found to carry a pathogenic germline BRCA1 mutation, this does not mean cancer is certain, but it does mean your lifetime risk of breast and ovarian cancer, and to a smaller extent some other cancers, is substantially higher than average. Your care team will typically recommend a personalised plan that may include earlier and more frequent breast screening (often including breast MRI in addition to mammography), consideration of risk-reducing surgery such as bilateral mastectomy or salpingo-oophorectomy, and referral to a genetic counsellor to discuss reproductive options and family testing.

If your tumour is found to carry a somatic BRCA1 mutation but germline testing is negative, this generally means your family members are not at increased inherited risk from this finding, but your own treatment plan may still be influenced, since somatic BRCA1 alterations can also predict benefit from PARP inhibitors and platinum chemotherapy in several cancer types.

If your result is a variant of uncertain significance (VUS), this is common and does not mean something is wrong with you or your report. It simply means the specific DNA change identified has not yet been proven to affect BRCA1 function or cancer risk. VUS results should not currently be used to guide surgery or screening decisions beyond what your family history would already suggest, and laboratories periodically reclassify variants as more evidence accumulates, so it is worth asking whether your report will be revisited over time.

BRCA1 testing does not diagnose cancer; it defines genetic risk or, in an already diagnosed tumour, molecular characteristics that inform treatment. In the risk-assessment setting, a positive germline result typically leads to a structured surveillance and prevention plan rather than an immediate diagnosis of disease. In the treatment setting, a pathologist or oncologist orders BRCA1 and related homologous recombination testing on tumour tissue alongside standard diagnostic workup, particularly for newly diagnosed high-grade serous ovarian cancer, where testing at diagnosis is now considered standard practice, and for certain breast cancers, especially triple-negative breast cancer or cancer diagnosed at a young age.

Germline BRCA1 testing is usually performed on a blood or saliva sample and analyses the gene in DNA that is present in all your cells, independent of any tumour. It is generally recommended after a discussion with a genetic counsellor or a clinician trained in cancer genetics, both to select the right test and to prepare for the range of possible results, including a VUS. Testing may be prompted by a personal history of breast cancer at a young age, triple-negative breast cancer, ovarian cancer at any age, male breast cancer, or a family history suggestive of a hereditary breast and ovarian cancer syndrome.

Somatic BRCA1 testing is performed directly on tumour tissue, often as part of a broader next-generation sequencing panel or a homologous recombination deficiency (HRD) test, particularly in ovarian cancer, where guidelines recommend testing at diagnosis to guide use of PARP inhibitors. Because a somatic test cannot distinguish a mutation that is truly tumour-only from one that also exists in the germline, a positive somatic BRCA1 result is generally followed by confirmatory germline testing to clarify whether the family needs further evaluation.

Both types of testing rely on next-generation sequencing methods capable of reading the full BRCA1 gene sequence, sometimes supplemented by tests that detect large rearrangements not picked up by standard sequencing. Results are reported as pathogenic, likely pathogenic, benign, likely benign, or variant of uncertain significance, and are usually returned within two to four weeks.

BRCA1 mutations are most strongly associated with breast cancer and ovarian cancer, but the pattern within each is distinctive. In breast cancer, BRCA1-related tumours are disproportionately triple-negative breast cancer, meaning they lack oestrogen receptor, progesterone receptor and HER2 overexpression; this subtype tends to be more aggressive and does not respond to hormonal therapy or HER2-targeted therapy, which is part of why BRCA1 testing is often recommended specifically in triple-negative disease. In ovarian cancer, BRCA1 mutations are strongly linked to high-grade serous ovarian cancer, the most common and typically most aggressive ovarian cancer subtype; a meaningful proportion of high-grade serous cases carry either a germline or somatic BRCA1/BRCA2 mutation.

Beyond breast and ovarian cancer, germline BRCA1 mutations are associated with a smaller but real increase in risk of prostate cancer and pancreatic cancer, and possibly some other cancers, which is why family history across generations and across cancer types is considered during genetic counselling. Somatic BRCA1 alterations, and the related biomarker homologous recombination deficiency (HRD), can also be found at lower frequency in a range of other tumours where their significance is still being studied.

For people newly diagnosed with a BRCA1-associated cancer, treatment usually still begins with the standard approach for that cancer type and stage — surgery, chemotherapy or radiotherapy as appropriate — with BRCA1 status layered in to refine chemotherapy choice and to determine eligibility for PARP inhibitor maintenance or treatment. In ovarian cancer, this commonly means platinum-based chemotherapy followed by consideration of a PARP inhibitor as maintenance therapy in appropriate candidates. In breast cancer, BRCA1 status may influence chemotherapy selection and can make a patient eligible for a PARP inhibitor, alongside standard local treatment.

For people who carry a germline BRCA1 mutation but do not currently have cancer, options centre on prevention rather than treatment: enhanced screening (such as annual breast MRI alongside mammography, starting earlier than average-risk guidelines recommend), risk-reducing surgery (bilateral mastectomy, and risk-reducing salpingo-oophorectomy typically once childbearing is complete and often around the time recommended by guidelines), and in some cases medication-based risk reduction discussed individually with a specialist. Because these decisions are personal and involve trade-offs around fertility, body image and timing, they are usually made over a series of conversations with a genetic counsellor, breast or gynaecological oncology specialist, and sometimes a mental health professional, rather than at a single appointment. Clinical trials are also increasingly relevant, since BRCA1 status and homologous recombination deficiency are common eligibility criteria for studies of newer targeted therapy combinations.