Unknown Primary Presenting With Axillary Lymphadenopathy

Abstract Breast cancer can rarely present as isolated axillary adenopathy without any evidence of a primary breast mass creating many diagnostic and therapeutic challenges. Occult breast cancer is defined as isolated axillary adenocarcinoma without detectable tumor in the breast by either physical examination or with imaging such as mammogram, ultrasound, or MRI. Occult breast cancer, although rare, has been acknowledged for more than 100 years. It was first described by Halsted in the Annuals of Surgery in 1906.