BRCA1 is a gene that provides instructions for building a protein whose main job is to repair damaged DNA and prevent cells from becoming cancerous. It belongs to a class of genes called tumor suppressors, which keep cell growth in check. When BRCA1 works properly, it acts as a kind of quality control system for your genetic code. When it doesn’t, the consequences can be serious.
How BRCA1 Repairs Damaged DNA
Every day, the DNA inside your cells sustains damage from normal metabolic processes, environmental exposures, and errors during cell division. One of the most dangerous types of damage is a double-strand break, where both rails of the DNA ladder snap at the same point. Left unrepaired, these breaks can cause cells to lose or rearrange genetic information in ways that lead to cancer.
BRCA1’s primary repair role involves a precise process called homologous recombination. When a double-strand break occurs, the BRCA1 protein coordinates with other repair proteins to use the intact copy of the chromosome as a template, essentially copying the correct sequence back into the broken strand. This is the most accurate way a cell can fix this type of damage. Without functional BRCA1, cells fall back on cruder, error-prone repair methods that introduce mutations, gradually destabilizing the genome.
Controlling When Cells Divide
DNA repair only works if the cell pauses long enough to actually fix the damage before copying itself. BRCA1 helps enforce these pauses, known as cell cycle checkpoints. When DNA breaks are detected, a signaling cascade activates BRCA1, which then helps halt the cell at critical stages of division. This gives the repair machinery time to work before the cell commits to splitting into two daughter cells.
If these checkpoints fail, a cell with broken DNA keeps dividing, passing damaged genetic material to its descendants. Over many rounds of division, the errors compound, and a normal cell can gradually acquire the traits of a cancer cell: uncontrolled growth, resistance to death signals, and the ability to invade surrounding tissue.
Regulating Other Genes
Beyond repair and checkpoint duties, BRCA1 also influences the activity of dozens of other genes. Research published in the Proceedings of the National Academy of Sciences found that when BRCA1 is active, it dials down two well-known growth-promoting genes: MYC (reduced 4.2-fold) and cyclin D1 (reduced 3.2-fold). Both of these genes are overexpressed in many breast tumors, so BRCA1’s ability to suppress them is one mechanism by which it keeps breast tissue growth in check.
At the same time, BRCA1 ramps up genes involved in immune signaling and cell communication. It also plays a role in embryonic development, interacting with a wide network of other proteins that regulate how cells specialize and organize into tissues. This broad reach helps explain why losing BRCA1 function has such far-reaching effects.
What Happens When BRCA1 Stops Working
A harmful mutation in BRCA1 doesn’t cause cancer directly. Instead, it removes one of the cell’s most important safety nets. Without accurate DNA repair, mutations accumulate faster than the cell can manage. Without functional checkpoints, damaged cells keep dividing. Without proper gene regulation, growth-promoting signals go unchecked.
The cancer risk is substantial. According to the National Cancer Institute, more than 60% of women who inherit a harmful BRCA1 change will develop breast cancer during their lifetime, compared to about 13% of women in the general population. The risk of ovarian cancer is also dramatically elevated, ranging from 39% to 58% over a lifetime for BRCA1 mutation carriers.
Breast and ovarian tissues seem especially vulnerable because they are highly responsive to hormones that drive cell division. More division means more opportunities for DNA damage, and without BRCA1 to clean up that damage, the odds of a cancerous transformation climb with each cell cycle.
Inherited vs. Acquired Mutations
BRCA1 mutations can be inherited (passed from a parent) or acquired (occurring spontaneously in a cell during a person’s life). Inherited mutations are present in every cell in the body from birth. You get two copies of the gene, one from each parent. If one copy is already broken, only the remaining working copy stands between you and the loss of BRCA1 function in any given cell. When that second copy is damaged by chance, repair capacity is lost entirely in that cell.
Certain populations carry BRCA1 mutations at higher rates. Three specific mutations occur frequently among people of Ashkenazi Jewish descent, enough that genetic testing is sometimes recommended even without a strong family history of cancer. In one study, 10% of Ashkenazi Jewish women diagnosed with breast cancer in their 40s carried one of these mutations.
How BRCA1 Status Shapes Treatment
Understanding what BRCA1 does has opened the door to targeted cancer therapies. The most important example is a class of drugs called PARP inhibitors. Here’s the logic: PARP is a protein that handles a different type of DNA repair. In normal cells, if you block PARP, the cell can still rely on BRCA1-driven repair as a backup. But in cells where BRCA1 is already broken, blocking PARP removes the last remaining repair pathway. The cancer cell accumulates so much DNA damage that it dies, while healthy cells with at least one working copy of BRCA1 survive.
This strategy, called synthetic lethality, has become a cornerstone of treatment for BRCA1-deficient cancers. Recent research suggests the toxicity of PARP inhibitors in these cells comes specifically from gaps that form during DNA replication, rather than from the double-strand breaks originally thought to be responsible. That distinction matters because it’s guiding the development of next-generation treatments and helping researchers understand why some tumors eventually become resistant.
Who Should Consider Genetic Testing
National guidelines recommend considering BRCA1 testing for people with specific personal or family histories. The criteria include being diagnosed with breast cancer at age 45 or younger, or having two or more close blood relatives with breast cancer at any age. A personal or family history of ovarian cancer, male breast cancer, or cancer in both breasts also raises the threshold for testing.
Testing involves a blood or saliva sample and typically returns results within a few weeks. A positive result doesn’t mean cancer is inevitable, but it does shift the math enough to change screening schedules, preventive options, and treatment decisions in meaningful ways. For people who carry a mutation, more frequent imaging, earlier screening, and preventive surgical options all become part of the conversation.