Collision tumors are rare clinical entities in which two histologically distinct tumor types show involvement in the same site. The occurrence of these tumors in the breast is extremely rare. Here, we present a case of a patient with both invasive ductal carcinoma and chronic lymphocytic leukemia in the breast. Wide excision with sentinel lymph node biopsy revealed palpably abnormal lymph nodes negative for breast carcinoma on frozen section. Histopathological examination of these lymph nodes showed extensive involvement by lymphoma and review of the breast specimen demonstrated the same lymphoma at the periphery of the ductal carcinoma. We review the literature and discuss possible etiologies for the dual presentation of both cancers.