A Collision Tumor With Features of Breast Cancer and Plasma Cell Myeloma as Primary Tumors

Abstract

Collision tumors, consisting of two different histological types of cancer, are rare but may have important implications, both for the patient and possibly in terms of cancer risks and predisposition. This patient has had prior invasive ductal breast cancer treated with surgery and chemotherapy 5 years earlier, but she developed a pathological hip fracture and anemia. The workup uncovered a plasma cell dyscrasia and the bone biopsy from the hip showed the collision tumor with an interface between breast cancer and plasma cell cancer. Such combination tumors may be diagnostic and therapeutic challenges, but they also raise significant questions regarding pathogenesis. Local factors such as neuro-immune crosstalk or cytokine perturbations may be at play. Alternatively, or in addition, oncogenic growth factors or the effects of prior chemotherapy may be significant.