Ventriculoperitoneal (VP) shunts are the standard treatment for hydrocephalus, and the distal catheter is often routed subcutaneously across the anterior chest wall. The development of ipsilateral breast cancer is rare, with fewer than 15 cases reported in the English literature, and there is no established consensus regarding the management of the shunt catheter during mastectomy. We report a 58-year-old shunt-dependent woman with a right-sided VP shunt placed for post-subarachnoid hemorrhage hydrocephalus, who was diagnosed with right breast cancer (cT2N1M0, stage IIB). Preoperative imaging demonstrated a 20 mm distance between the medial edge of the tumor and the catheter, which was judged sufficient to allow shunt preservation. A right total mastectomy with axillary lymph node dissection was performed with a neurosurgeon on standby. Energy devices were avoided in the vicinity of the catheter, and sharp dissection was performed with Metzenbaum scissors. The catheter was preserved without damage, and strict aseptic technique was maintained throughout. Adjuvant chemotherapy and post-mastectomy radiotherapy (PMRT) were administered uneventfully after multidisciplinary planning, and the patient remains free from recurrence under ongoing endocrine therapy with abemaciclib. Total mastectomy with VP shunt preservation can be safely accomplished when a sufficient tumor-catheter margin is confirmed preoperatively and when meticulous intraoperative technique and multidisciplinary collaboration covering PMRT planning are ensured.