Factors Influencing Management and Outcome in Patients with Occult Breast Cancer with Axillary Lymph Node Involvement: Analysis of the National Cancer Database

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.