Microangiopathic Hemolytic Anemia and Thrombocytopenia in Patients With Cancer

The unexpected occurrence of thrombotic microangiopathy (TMA), characterized by microangiopathic hemolytic anemia and thrombocytopenia, in a patient with cancer requires urgent diagnosis and appropriate management. TMA is a term used to describe multiple syndromes caused by microvascular thrombosis, including thrombotic thrombocytopenic purpura (TTP), Shiga toxin-mediated hemolytic uremic syndrome, and complement-mediated TMA. In patients with cancer, systemic microvascular metastases and bone marrow involvement can cause microangiopathic hemolytic anemia and thrombocytopenia. This occurs most often in patients with known metastatic cancer, but microangiopathic hemolytic anemia and thrombocytopenia may occur unexpectedly in patients without known metastatic disease or be the presenting features of undiagnosed cancer. TMA may also be caused by commonly used chemotherapy agents, either through dose-dependent toxicity or an acute immune-mediated reaction. These causes of TMA must be distinguished from TTP, which results from a severe deficiency of ADAMTS13 and is the most common cause of TMA among adults without cancer. The importance of this distinction is to avoid inappropriate use of plasma exchange, which is associated with major complications. Plasma exchange is the essential treatment for TTP, but it has no known benefit for patients with cancer-induced or drug-induced TMA. We will describe cancer-induced and drug-induced TMA using the experience of the Oklahoma TTP-Hemolytic Uremic Syndrome Registry and data from a systematic review of all published reports of drug-induced TMA. We will illustrate the principles of evaluation and management of these disorders with patients' stories.