A woman in her 50s presented to the emergency department with acute, severe, left flank pain. There was no medical history of trauma, fever, or hematuria. She was receiving therapy for mantle cell lymphoma and had previously undergone 1 cycle of the Nordic protocol (comprising cyclophosphamide, doxorubicin, vincristine, prednisolone, cytarabine, and rituximab).1 However, this resulted in tumor lysis syndrome and neutropenic sepsis. The patient was reluctant to undergo further infusional therapy and was switched to ibrutinib, 560 mg, once daily. During the 2-month period that she was receiving ibrutinib therapy, there were no concurrent administrations of anticoagulants. At presentation, she was hypotensive (blood pressure, 79/45 mm Hg) with conjunctival pallor and left renal angle tenderness. The patient’s hemoglobin count was low (7.6 g/dL; reference range, 12-16 g/dL; to convert to g/L, multiply by 10.0), which represented a significant decrease from the baseline (10.6 g/dL) measured 1 month before presentation. She was also found to have acute-onset thrombocytopenia (40×109/L; reference range, 140-400×109/L) and leukocytosis (12.75×109/L, reference range, 4-10×109/L). Her coagulation profile (prothrombin time) was normal. A computed tomographic (CT) scan of the abdomen and pelvis was performed (Figure 1A) and compared with a similar scan performed 4 months prior (Figure 1B).