Background: Occult breast cancer (OBC) is rare and optimal local–regional (LR) management has not been defined. Using a patient registry database, we examine factors associated with treatment and outcomes in OBC. Methods: Female patients with cT0 N1/2 M0 BC were selected from the National Cancer Database (2004–2013) and categorized into four treatment groups: MAST = mastectomy with axillary lymph node dissection (ALND) ± radiation (RT); RT + ALND = RT with ALND, no breast surgery; ALND = ALND alone; OBS = no breast surgery, RT, or ALND. Patient characteristics and overall survival (OS) were compared between groups, and multivariable analysis was used to identify factors associated with treatment and OS. Results: Among 2.03 million BC cases, 1853 females (0.09%) with cT0 N1/2 M0 disease were identified and 1231 patients were categorized into a treatment group: MAST = 592, RT + ALND = 342, ALND = 106, OBS = 191. On logistic regression, care at an academic center was associated with a higher likelihood of RT + ALND compared with MAST (odds ratio 2.03, 95% confidence interval [CI] 1.50–2.74, p < 0.001). Patients treated with RT + ALND had significantly better OS on univariate survival analysis compared with patients treated with MAST (hazard ratio [HR] 0.475, 95% CI 0.306–0.736, p = 0.001). RT + ALND was independently associated with OS on multivariable survival analysis (HR 0.509, 95% CI 0.321–0.808, p = 0.004), after adjusting for covariates. Conclusions: Patients with OBC were more likely to undergo RT + ALND if they received care at an academic center. Patients treated with RT + ALND had significantly better OS compared with patients treated with MAST, after adjusting for covariates. This supports the use of RT + ALND as LR treatment for patients with OBC.
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