Gene Mutation

Genes are stretches of DNA that contain instructions for making proteins — the molecules that carry out virtually every function in the body. A gene mutation is a change in the sequence of chemical letters (nucleotides) that makes up a gene. That change might involve a single letter being swapped for another (a point mutation), a short sequence being deleted or duplicated, or larger rearrangements of DNA. Depending on where in the gene the change falls and what protein is affected, a mutation may have no effect, a subtle effect, or a major one.

Mutations are either germline (inherited) or somatic (acquired). Germline mutations are present in every cell of the body from conception, because they were inherited from one or both parents via egg or sperm. They can be passed on to children. BRCA1 and BRCA2 mutations are the most well-known examples: inheriting a harmful mutation in either gene significantly raises lifetime risk of breast and ovarian cancer. Somatic mutations occur in individual cells during a person's lifetime — through errors in DNA copying during cell division or through damage from environmental exposures like UV radiation, tobacco carcinogens, or certain chemicals. Somatic mutations are not inherited.

Cancer almost always involves the accumulation of multiple somatic mutations in the same cell or cell lineage. These mutations typically affect genes that control cell growth and division — either by disabling tumor suppressor genes (which normally put brakes on cell proliferation) or by permanently activating oncogenes (which accelerate it). Understanding which specific mutations are present in a tumor increasingly guides treatment, as many targeted therapies are designed to block the effects of specific mutated proteins.

The concept of gene mutations helps explain why cancer runs in some families, why not everyone who smokes gets lung cancer, and why two people with "the same" breast cancer may respond very differently to treatment. Cancer is, at its core, a disease of accumulating genetic change — which means that understanding the genetic landscape of a tumor gives doctors an increasingly precise map for treatment.

For inherited mutations, genetic testing offers the ability to act before cancer develops. People who learn they carry a BRCA1 or BRCA2 mutation can work with their doctors on enhanced surveillance, preventive medications, or risk-reducing surgery. That kind of foresight is powerful. Genetic counseling before and after testing helps people interpret results in the context of their own family history and make decisions that reflect their values — which is exactly the kind of individualized, informed approach that leads to better outcomes.