Bone Marrow Failure in Prostate Cancer: A Rare Case Initially Disguised as Thrombotic Thrombocytopenic Purpura

Prostate cancer is the second most common cause of cancer-related death and the leading cause of new cancer cases in men in the United States. Bone trabeculae are the most common site of metastasis for prostate cancer, but bone marrow (BM) involvement is rare. Around six percent of patients with new metastatic castrate-sensitive prostate cancer (mCSPC) have biopsy-proven BM metastasis. We present a case of mCSPC with BM metastasis initially disguised as thrombotic thrombocytopenic purpura (TTP). Initial presentation revealed anemia and thrombocytopenia with a peripheral blood smear indicating thrombotic microangiopathy. Empiric treatment for TTP was initiated, but the patient showed no improvement. A BM biopsy performed on hospital day 5 for further work-up of the refractory cytopenias eventually identified metastatic prostate adenocarcinoma. The patient started androgen deprivation therapy, but attempts at follow-up care were unsuccessful. The patient passed away five months later. This case highlights the diagnostic complexity of cytopenias and contributes to our understanding of BM-metastatic prostate cancer. BM involvement in mCSPC complicates prognosis, and further research into its pathophysiology and targeted therapies is needed to improve patient outcomes.