The effect of local therapy on breast cancer-specific mortality of women with occult breast cancer and advanced nodal disease (N2/N3): a population analysis.

Purpose: Current NCCN guidelines for occult breast cancer (OBC) recommend modified radical mastectomy, with the option for breast preservation with radiation instead of mastectomy for N1 patients. Our aim was to compare the effect of local therapy-mastectomy versus breast radiation-on breast cancer-specific mortality (BCSM) in a contemporary cohort of OBC patients of all nodal stages.

Methods: Competing risk analyses were performed to evaluate the effect of local therapy, nodal stage, and other demographic and clinical prognostic variables on risk of BCSM for women registered in the SEER database with T0N+M0 breast cancer from 2004 to 2015.

Results: Of the 353 women with OBC who underwent axillary nodal dissection, 152 received breast radiation and 201 underwent mastectomy. Overall, 57.5% had N1 disease, 54.4% had estrogen receptor (ER) positive tumors, 80.7% were white, and 88.1% received chemotherapy. Women treated with radiation were older (p < 0.001). The two groups were comparable with respect to all other variables analyzed. During a median follow-up of 66 months, 32 women died from breast cancer (radiation: 11, mastectomy: 21). Five-year cumulative incidence of BCSM was 8.0% ± 2.6% with radiation versus 10.9% ± 2.6% with mastectomy (p = 0.309). On multivariate analysis, independent predictors of BCSM included older age, higher N stage, and ER negativity, but the type of local therapy was not significantly associated with outcome.

Conclusions: These results suggest that breast preservation is a reasonable alternative to mastectomy for OBC patients, regardless of nodal stage.