Vagus nerve stimulation (VNS) was approved for the management of intractable partial epilepsy in patients 12 years of age and older in 1997.1 The device was also approved in 2005 for treatment-resistant depression. The pulse generator is typically placed in the left pectoral region for stimulation of the left vagus nerve.1 We present two patients who had undergone chronic VNS and developed adenocarcinomas of the breast anatomically related to the pulse generators. The diagnostic yield of breast self-examination and mammography to identify early stages of breast cancer may be reduced by VNS. ### Patient 1. A 34-year-old woman had a VNS device implanted in 2003 for management of intractable partial epilepsy related to a large multilobar malformation of cortical development. The patient palpated a firm mass in 2006 under the pulse generator in the left pectoral region. An ultrasound of the left breast revealed an 8.8 cm by 11.5 cm mass. Biopsy indicated an invasive ductal carcinoma. The patient was treated …