A Negative BRCA1 Test in a Woman With Early-Onset Triple-Negative Breast Cancer
A 38-year-old woman is diagnosed with triple-negative breast cancer. Her mother had high-grade serous ovarian cancer at 52 and carries a pathogenic BRCA1 variant (c.5266dupC). The patient undergoes targeted testing for the familial variant and is negative. She has two daughters, ages 8 and 11, and asks whether they are “in the clear” and whether she should have “the full test.” Her tumor is ER/PR/HER2 negative, grade 3, with no family history of male breast cancer or pancreatic cancer. The genetic counselor notes that the patient’s father is 70 and healthy.
1. Interpret the negative targeted test and list the possible explanations.
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A negative targeted test for the known familial BRCA1 variant is generally reliable and means the patient did not inherit that variant. However, her early-onset triple-negative breast cancer still requires an explanation. Possibilities include: (1) phenocopy-her cancer is sporadic, and the mother’s BRCA1 variant is not the cause of this patient’s tumor; BRCA1 carriers have a 50% transmission risk, so not every cancer in a family is attributable to the variant; (2) a different hereditary predisposition, such as BRCA2, PALB2, BARD1, RAD51C, or RAD51D, which are associated with triple-negative breast cancer; (3) a rare technical or clerical error, which is unlikely with a validated assay but should be considered if the family history is strong; and (4) a somatic-only event, which would not explain a germline predisposition.
2. What additional germline testing, if any, is indicated for the patient, and what are the implications for her daughters?
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Because of her young age at diagnosis and triple-negative subtype, she meets criteria for a multigene germline panel regardless of the negative BRCA1 result. The panel should include BRCA1, BRCA2, PALB2, and other breast cancer genes. If the panel is negative, her daughters do not inherit the maternal BRCA1 variant and should follow population-based breast awareness and screening recommendations; they do not need BRCA1-specific surveillance. They should not be tested as children. If a different pathogenic variant is found, the daughters can be offered predictive testing in adulthood. If the panel is negative, the patient’s residual hereditary risk is reduced but not zero, and she should be managed according to her cancer treatment and survivorship guidelines.
3. How do you counsel about the mother’s BRCA1 variant and the patient’s own cancer?
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Explain that the patient did not inherit her mother’s BRCA1 variant, so she is not at BRCA1-associated risk and her daughters are not at risk for that variant. However, her own cancer may still have a genetic cause, and a multigene panel is appropriate. Discuss that a negative panel does not prove no genetic risk, and that her daughters’ risks will be based on her result and family history. Emphasize that the mother’s BRCA1 variant remains important for the mother’s own surveillance and for other relatives on that side of the family. Offer psychosocial support and clarify that the patient’s cancer treatment, including PARP inhibitor eligibility, depends on tumor testing rather than the germline result.