Understanding BRCA & Other Hereditary Cancer Variants
BRCA1 and BRCA2 are the best-known hereditary-cancer genes, but a modern panel reads many more — PALB2, CHEK2, ATM, and the Lynch-syndrome mismatch-repair genes among them. This guide explains what these genes do, how a variant is classified, and what a result can and cannot tell you.
Hereditary Cancer Genetics
Most hereditary-cancer genes are DNA-repair genes
BRCA1, BRCA2, PALB2, CHEK2, and ATM all participate in the cell's machinery for repairing damaged DNA — particularly double-strand breaks, repaired through a high-fidelity process called homologous recombination. When one copy of such a gene carries a pathogenic variant from birth, the cell still functions normally because the second, working copy keeps repair intact. Cancer risk rises over a lifetime because, in occasional cells, the remaining working copy is lost or damaged, leaving that cell less able to repair DNA accurately. The Lynch-syndrome genes (MLH1, MSH2, MSH6, PMS2, and the related EPCAM) work in a different repair pathway — mismatch repair, which proofreads errors made when DNA is copied.
This mechanism explains an important point: inheriting a pathogenic variant does not mean cancer has begun, or that it is certain to. It means one layer of a multi-layered safeguard is reduced from the start, which is why risk is elevated but never absolute.
Autosomal dominant inheritance, variable penetrance
These genes are inherited in an autosomal dominant pattern: a person with a pathogenic variant has a 50% chance of passing it to each child, and the variant can come from either the mother's or the father's side. Because it is dominant at the level of inheritance, a single copy is enough to confer elevated risk — which is also why family history on either side matters.
Penetrance describes how often a variant actually leads to disease over a lifetime, and it differs sharply by gene. A pathogenic BRCA1 variant carries a high lifetime risk of breast and ovarian cancer; a pathogenic CHEK2 or ATM variant typically confers more moderate risk. Penetrance is also shaped by other genetic factors, age, sex, and environment — which is why two people with the same variant can have very different outcomes, and why management is individualized rather than one-size-fits-all.
What pathogenic, benign, and uncertain mean
Laboratories classify each variant along a five-tier scale established by the American College of Medical Genetics and Genomics (ACMG). The label reflects the strength of evidence that a variant affects gene function — not a measure of how aggressive any future cancer might be.
Pathogenic / Likely pathogenic
Strong evidence the variant disrupts the gene's function and meaningfully raises cancer risk. This is the result that informs screening and prevention plans. It predicts elevated risk over time — it does not mean cancer is present or inevitable, and it says nothing about timing.
Benign / Likely benign
Strong evidence the variant does not affect function. These are common in everyone's genome and are not reported as findings that change care. A benign result in one gene does not rule out risk from genes not tested or from non-genetic factors.
Variant of uncertain significance (VUS)
The evidence is incomplete — the variant may or may not affect function. A VUS is not a 'positive' result and generally should not drive surgical or screening decisions on its own. Most VUS findings are eventually reclassified as benign as more data accumulates.
Reclassification over time
Variant interpretation is a living, evolving science. As laboratories pool more population data, family studies, and functional experiments, classifications are updated — sometimes a VUS becomes benign, occasionally pathogenic. This is why staying connected to the testing lab and care team matters after a result.
Frequently asked questions
If I carry a pathogenic BRCA variant, will I definitely get cancer?
No. A pathogenic variant raises lifetime risk, sometimes substantially, but risk is a probability, not a certainty. Penetrance is variable, and effective screening and risk-reducing options exist. The result is a tool for planning, not a diagnosis or a prediction of when anything will happen.
What is the difference between BRCA and the Lynch-syndrome genes?
BRCA1, BRCA2, PALB2, CHEK2, and ATM mainly repair double-strand DNA breaks and are most associated with breast and ovarian cancer (with other associations varying by gene). The Lynch-syndrome genes — MLH1, MSH2, MSH6, PMS2, and EPCAM — work in mismatch repair and are most associated with colorectal and endometrial cancer. Different mechanism, different gene set, different screening implications.
I received a 'variant of uncertain significance.' Should I be worried?
A VUS is genuinely uncertain — it is not evidence of elevated risk, and clinical guidelines advise against making major medical decisions based on a VUS alone. Most VUS findings are later reclassified as benign. Your care team will typically manage based on personal and family history while the variant's classification is reviewed over time.
Does a negative result mean I have no hereditary risk?
Not entirely. A negative panel means no pathogenic variant was found in the genes tested. Hereditary risk can still come from genes outside the panel, from variants current methods cannot detect, or from a strong family history that warrants screening regardless of genetics. A genetic counselor can interpret a negative result in the context of your full history.
Who interprets these results?
Variant classification is performed by clinical laboratory scientists against established evidence frameworks, and results are interpreted for the individual by genetics professionals — genetic counselors and physicians — who place them in the context of personal and family history. Interpretation is a clinical judgment, not a number a test reads out on its own.
Genetics is most useful when it's understood, not just reported
If a panel result has raised questions — about a gene you hadn't heard of, a variant of uncertain significance, or what a finding means for your family — clear, unhurried explanation is the next step. Reach out and we'll help you find the right reference or professional guidance.