Acute Lymphoblastic Leukemia in a Patient Treated with Letrozole and Palbociclib.

Palbociclib, in conjunction with endocrine therapy, has been approved for the treatment of patients with advanced breast cancer. The common hematological toxicities associated with palbociclib are leukopenia and neutropenia. However, hematological malignancies have not been reported for palbociclib treatment. Here, for the first time, we present a case of acute lymphoblastic leukemia that was diagnosed in a patient undergoing treatment with letrozole and palbociclib for metastatic breast cancer. This case emphasizes the need for long term follow up of patients treated with palbociclib.