Bone marrow metastasis of prostatic adenocarcinoma with post-treatment foamy-like changes: A diagnostic pitfall

Prostatic acinar adenocarcinoma (PAA) is the most common malignant tumour of the male genital system. Hormonal therapy and radiotherapy are widely-used treatment modalities in advanced stage disease. However, with hormonal therapy, the morphology of the neoplastic cells can be altered with a shift towards benign-appearing cells with inconspicuous nucleoli and abundant cytoplasm. When the tumour spreads to the bone marrow, these neoplastic cells can mimic foamy histiocytes, which may lead to a misdiagnosis. This becomes more challenging if a concurrent bone marrow malignancy is identified. Attention should be paid if foamy cells are detected in bone marrow, particularly if the patient has a history of PAA. To the best of our knowledge, this is the first report of simultaneous bone marrow involvement by metastatic PAA with mimicking foamy histiocytes and lymphoplasmacytic lymphoma.