Breast cancer is a common health concern, and a family history of the disease often leads to questions about personal risk. When multiple relatives are diagnosed, many people wonder if the predisposition to the disease can bypass one generation and appear in the next, a phenomenon often described as “skipping generations.” The concept of an inherited risk appearing to skip a generation is biologically possible, stemming from the complicated ways genetic changes are passed down and expressed.
Understanding the Genetics of Skipping Generations
The idea that breast cancer itself skips a generation is misleading, but the appearance of this pattern is a direct result of how high-risk genes are inherited. Genes responsible for a significantly increased risk, such as BRCA1 and BRCA2, are passed down in an autosomal dominant pattern. This means a child has a 50% chance of inheriting the altered gene copy from a parent who carries the mutation.
If a parent carries a mutation but never develops cancer, they are still capable of passing that genetic change to their child. This is explained by a concept called penetrance, which is the likelihood that a person with a specific gene mutation will actually develop the disease. High-risk mutations like BRCA1/2 have high, but incomplete, penetrance, meaning that not every carrier will get cancer.
For example, a grandmother with a BRCA mutation may develop breast cancer and pass the mutation to her son, who may never develop the disease in his lifetime. If that son then passes the mutation to his daughter, and she is later diagnosed, the cancer appears to have skipped the middle generation. The gene mutation itself did not skip the son; rather, the cancer did not manifest in him. The son remained a carrier, unknowingly transmitting the genetic susceptibility to his child.
Distinguishing Hereditary from Sporadic Cancer
A family history of breast cancer does not automatically mean a high-risk mutation is present. The vast majority of breast cancers (approximately 90%) are classified as sporadic, resulting from random genetic mutations acquired over a lifetime. These cases do not involve a clear inherited risk that runs through the family line.
Conversely, hereditary breast cancer (about 5% to 10% of all cases) is caused by germline mutations passed down from a parent. These inherited mutations significantly increase the lifetime risk for cancer. Hereditary cases often involve diagnosis at a younger age or multiple cancers in the same individual.
A third category is familial cancer, which describes a concentration of cancer cases in a family that does not fit the pattern of a known high-risk mutation. In these situations, the increased risk may be due to a combination of shared lifestyle factors, common environmental exposures, or inherited changes in genes with lower penetrance. Understanding this distinction is helpful, as the “skipping generations” question applies almost exclusively to the rare, high-risk hereditary forms of the disease.
Steps for Personal Risk Assessment
For individuals concerned about their family history, the first step in risk assessment involves collecting a thorough health history from both the maternal and paternal sides of the family. Gathering details about the type of cancer, age of diagnosis, and relationship of affected relatives is important, as risk can be inherited from either parent. This history provides the foundation for determining if a family meets the criteria for further investigation.
A medical professional may recommend genetic counseling, which involves a conversation with a trained expert to evaluate the family history and discuss the likelihood of an inherited mutation. The counselor explains the implications of genetic testing and helps the individual weigh the benefits and limitations of the process. Genetic counseling is generally recommended before any testing takes place.
Genetic testing is not appropriate for everyone and is typically reserved for those who meet specific criteria suggesting a high probability of a mutation. These criteria include:
- Having a close relative with a known mutation.
- A diagnosis of breast cancer before age 50.
- Multiple relatives with breast or ovarian cancer.
- A diagnosis of male breast cancer.
If a mutation is found, the results enable personalized surveillance and risk-management strategies, which may include enhanced screenings or preventative measures.