Acute myeloid leukemia with an unusual histologic pattern mimicking metastatic carcinoma in bone marrow: a diagnostic pitfall

We describe two cases of acute myeloid leukemia with an unusual histological pattern mimicking metastatic non-hematopoietic neoplasm, leading to diagnostic difficulties. Both patients presented with pancytopenia and absence of circulating blasts. Bone marrow aspirations were not successful. Bone marrow core biopsies contained neoplastic cells arranged in cohesive sheets or single file patterns with prominent myxoid stroma resembling metastatic carcinoma. The accompanying bone marrow touch imprints showed clusters of immature cells with monocytoid features. The cell lineage was further revealed by immunohistochemical analysis of bone marrow core biopsy sections. The neoplastic cells showed strong reactivity for myeloperoxidase, CD33, CD43, CD45, and CD68, indicating a myeloid cell origin with monocytic differentiation. One patient (age, 39 years) received standard chemotherapy for acute myeloid leukemia, which resulted in remission of bone marrow disease. The other patient (age, 85 years) died with multiple organ failure before treatment. Failure to recognize these unusual histological features of acute myeloid leukemia could result in misdiagnosis from bone marrow biopsy.