A unique case of mixed phenotype acute leukemia with t(9;22)(q34.1;q11.2); BCR-ABL1 sarcoma with epitheliotropism mimicking intestinal T cell lymphoma

Abstract

Myeloid sarcomas and extramedullary manifestations of mixed phenotype acute leukemia (MPAL) without leukemic involvement are rare. We present an unusual case of myeloid sarcoma of T/myelomonocytic biphenotypic nature and BCR-ABL1 translocation demonstrating an epitheliotropism in the gastrointestinal tract and mass-forming lesions in the lungs without bone marrow involvement. A 69-year-old gentleman presented with non-bloody diarrhea and abdominal pain complicated by weight loss. CT scan showed diffuse mural thickening in the jejunum, distal ileum, transverse colon, and splenic flexure and bilateral pulmonary nodules. Biopsies of the ileum and colon were performed. An initial diagnosis of T cell lymphoma was made based on intestinal infiltration with CD4 and CD7 positive monomorphic atypical cells. Despite treatment, the patient's lung masses grew. A comprehensive immunohistochemistry panel was performed on the lung biopsy based on the classic morphologic appearance of sheets of atypical cells and that CD4 and CD7 are also expressed in a subset of myeloid cells. The panel demonstrated CD34 (subset), CD68, muramidase/lysozyme, and CD117 expressions. Flow cytometry showed an aberrant myelomonocytic population. The presence of T lineage blasts was confirmed by a subset of blasts with cytoplasmic CD3. The diagnosis of mixed phenotype T/myeloid sarcoma with myelomonocytic differentiation and t(9;22)(q34.1;q11.2);BCR-ABL1 was made. Epitheliotropism has not been previously described as a histologic feature of intestinal myeloid sarcomas. The epitheliotropism, enteropathy-like features and gastrointestinal symptoms mimicked T cell lymphomas. This case highlighted the pivotal role of flow cytometry and clinicopathological correlation in making a diagnosis of myeloid sarcoma with MPAL phenotype.

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