Breast cancer is complex, and a diagnosis involving a specific marker, like HER2-positive status, often raises questions about family risk. The human epidermal growth factor receptor 2 (HER2) protein is a growth-promoting receptor found on the surface of all breast cells. When breast cancer is classified as HER2-positive, the tumor cells have an excess of this protein, which drives aggressive cell growth. This naturally leads patients and their families to wonder if this particular subtype of cancer can be passed down. The answer requires distinguishing between genetic events that happen in a single cell versus those inherited from a parent.
What HER2 Status Means for the Tumor
HER2-positive status is a characteristic of the tumor itself, not an inherent trait of the patient’s entire body. The HER2 protein is produced by the HER2 gene, and in a healthy cell, this gene provides normal growth instructions. However, in approximately 15% to 20% of breast cancers, the HER2 gene malfunctions within the developing tumor cell.
This malfunction is typically a process called gene amplification, where the cell makes many extra copies of the HER2 gene. These additional gene copies instruct the cell to produce a vastly excessive amount of HER2 protein receptors on its surface, leading to uncontrolled growth and division. This amplification is considered an acquired event that occurs randomly as the tumor develops, separate from the genes a person inherits at birth. Because the overabundance of HER2 protein accelerates cell division, HER2-positive tumors can grow and spread more rapidly than HER2-negative tumors, although they often respond favorably to targeted therapies.
The Difference Between Inherited and Acquired Cancer
To understand the hereditary risk of HER2 cancer, it is important to distinguish between inherited and acquired genetic changes. Inherited, or germline, mutations are present in every cell of the body because they are passed down from a parent. These germline mutations significantly increase a person’s lifetime risk of developing cancer, but they do not guarantee a diagnosis. Only about 5% to 10% of all breast cancers result directly from such inherited gene changes, such as those in the BRCA1 or BRCA2 genes.
In contrast, acquired, or somatic, mutations occur only within the cancer cells and are the result of damage or errors that happen throughout a person’s lifetime. These changes are confined to the tumor tissue and are not present in the reproductive cells, meaning they cannot be passed on to children. The gene amplification that causes a tumor to become HER2-positive is overwhelmingly a somatic event.
Therefore, the specific HER2-positive status of a breast cancer is not an inherited trait. The tumor’s HER2 status is a genetic characteristic of the cancer itself, not a marker of an underlying inherited risk that runs in the family.
Linking Inherited Risk Genes to HER2 Status
While the HER2 status itself is not inherited, an inherited risk gene can increase the overall likelihood of developing breast cancer. A person with a BRCA1 or BRCA2 mutation has a higher chance of developing breast cancer, but that genetic predisposition does not dictate the tumor’s subtype. Breast cancers associated with the BRCA1 gene are most often triple-negative, meaning they lack estrogen receptors, progesterone receptors, and are HER2-negative.
For those with BRCA2 mutations, the resulting tumors are more heterogeneous but are less likely to be HER2-positive compared to sporadic, non-inherited cancers. Studies pooling data on cancers in BRCA1 and BRCA2 carriers show that the rate of HER2-positive status is low, often around 9% or less. This suggests that inherited cancer risk genes do not strongly favor the HER2-positive subtype. The family history indicates a general risk for cancer, but the specific HER2 protein over-expression is a separate, acquired event.
When Genetic Testing is Recommended
Genetic testing is not typically recommended based on a HER2-positive diagnosis alone, since that status is usually acquired. Instead, testing is guided by patterns in a person’s personal and family history that suggest an inherited risk for cancer.
This includes being diagnosed with breast cancer at a younger age, generally 50 or under, or having a triple-negative breast cancer diagnosis at any age. Testing is also recommended if there is a clustering of related cancers in the family, such as multiple instances of breast, ovarian, pancreatic, or high-risk prostate cancer on the same side of the family. A personal or family history of male breast cancer is also a strong indicator for genetic counseling and testing.
The goal of genetic testing is to identify a germline mutation that affects cancer screening and prevention for the entire family, which is a broader concern than the specific HER2 status of a single tumor.