Genetic testing referral and germline pathogenic variants in patients with breast cancer and another non-breast cancer.

Background: Guidelines recommend germline genetic testing for specific combinations of primary cancers and ages of diagnoses, but do not recommend testing for all patients with multiple primary cancers (MPC). Patients with breast cancer are more likely to receive genetic testing. Here, we evaluated whether a first breast cancer was more likely than another first cancer type to prompt testing referral.

Methods: Using Oncoshare, a breast cancer research database of medical records and the California Cancer Registry, we identified female patients with MPC diagnosed January 2000-June 2023 with breast cancer as either the first or second cancer and seen at Stanford Health Care. We analyzed genetic testing rates after first versus second cancer diagnosis and the yield of pathogenic variants (PV). We evaluated the association between the receipt of genetic testing and timing of breast cancer (1st or 2nd), using univariate and multivariable logistic regression adjusted for age at first diagnosis, race/ethnicity, and time between first and second diagnoses.

Results: 1,069 patients met eligibility criteria; 75 % were non-Hispanic white, and 73 % had breast as the first cancer. 342 (32 %) patients had testing, of which 113 (33 %) had at least one PV. Patients with first breast cancer had a trend toward higher testing rate, (OR 1.62, 95 % CI 0.9-3.0), p = 0.11.

Conclusion: Using a breast cancer research database, MPC patients showed a trend toward being more likely to receive genetic testing when breast cancer preceded another cancer. High yield for a germline pathogenic variant suggests that all MPC patients should have cancer genetics risk assessment.