Determine the positive predictive value (PPV) of biopsy of palpable masses following mastectomy (MX). Determine if there are patient characteristics, tumor, or imaging features more predictive of cancer. IRB-approved retrospective review of 16 396 breast ultrasounds June 2008-December 2015 identified patients with MX presenting with palpable masses. Medical records and imaging studies were reviewed. Statistical analysis was performed using Fishers exact test. 95% confidence intervals (CI) were calculated. In all, 117 patients presented with palpable masses on the MX side. 101/117 patients who had a palpable mass on physical examination had a true sonographic mass to correlate with the clinical findings. 91/101 (90%) underwent biopsy: 19/91 (21%, 95% CI; 13-31) biopsies were malignant. 72/91 (79%) were benign. All 19 cancers were on the original cancer side. Recurrences ranged from 0.4 to 4.5 cm maximum diameter, mean 1.3 cm. Prophylactic vs therapeutic mastectomy was very statistically significant (P = .01). The use of tamoxifen or an AI was also statistically significant (P = .04). Patient age (P = 1.0), radiation therapy (P = 1.05), chemotherapy (P = .2), immediate breast reconstruction (P = .2), or implant vs flap (P = .2) had no statistically significant association with finding cancer on biopsy. Lesion shape (irregular vs oval/round) was highly statistically significant (P = .0003) as was non-parallel orientation on ultrasound (P = .008). Circumscribed vs non-circumscribed margins was also statistically significant (P = .008). The PPV of biopsy of palpable masses on the side of MX was 21% (95% CI; 13-31). All recurrences were on the original cancer side and this was very statistically significant
