Multigene Germline Testing in Patients with DCIS vs Invasive Breast Cancer in a Large, Integrated Health Care System.

BACKGROUND

Identification of germline pathogenic (PV) and likely pathogenic variants (LPV) can inform patients of their risk for breast cancer, empowering them to utilize risk-reducing strategies. National guidelines for germline testing are the same for invasive breast cancer (IBC) and ductal carcinoma in situ (DCIS); however, data on how testing and results compare for patients with DCIS versus IBC are limited.

METHODS

This retrospective cohort study of multigene panel germline testing compared women with DCIS versus stage I-III IBC diagnosed between September 2019 through September 2022 at Kaiser Permanente Northern California.

RESULTS

Of the 1490 patients with DCIS and 8474 patients with IBC, the percentage of patients who underwent genetic testing was higher in those with IBC (38%, n = 3223) than in those with DCIS (28.5%, n = 424) (p < 0.00001). Among tested patients, the prevalence of PV/LPV in any breast cancer-related (BCR) gene was higher for IBC (9.1%) than for DCIS (6.1%) (p=0.041). The prevalence of PV/LPV in moderate-risk genes was similar (3.4% in IBC and 3.3% in DCIS; p=0.8798), whereas the prevalence in high-risk genes was higher for patients with IBC (5.8%) than for those with DCIS (3.1%) (p =0.0189).

CONCLUSIONS

Although the prevalence of PV/LPV in high-risk BCR genes was lower in DCIS than in IBC, the prevalence of PV/LPV was similar in moderate-risk BCR genes. Our study supports continuing the same genetic testing guidelines for DCIS and IBC since carrying a PV/LPV in a moderate-risk BCR gene will affect treatment and surveillance decisions.