Track

Case Reports

Abstract

A 67-year-old male with history of NPM1 mutated Acute Myeloid Leukemia status post chemotherapy and hematopoietic stem cell transplant after leukemia cutis relapse currently presented for routine follow-up. The bone marrow biopsy demonstrated a normocellular marrow with maturing trilineage hematopoiesis and a small cluster of immature cells. The differential diagnosis included a focus of leukemic blasts, erythroid precursors, or plasmacytoid dendritic cells. Immunostains showed positivity for CD117, CD71, and negativity for CD34, ERG, p53, Glycophorin-A and CD123. The small focus was lost of on deeper sections, hence definitive diagnosis could not be rendered. In addition, molecular minimal residual disease analysis for NPM1 was negative and total post-transplant chimerism showed 4% recipient and 96% donor genetic recombination.

Soon thereafter peripheral blood flow cytometry was performed, and revealed a distinct population of CD56 positive, CD117 dim-negative, CD45 negative events favoring circulating tumor cells of neurodendocrine crest origin. Repeat bone marrow biopsy demonstrated florid involvement by small cell neuroendocrine carcinoma diffuse positivity for synaptophysin and chromogranin. Additional detailed clinical history investigation revealed the presence of several dermal based lesions upper and lower extremities. Skin biopsy revealed a small round blue cell tumor that was positive for AE1/AE3, CK20 (dot-like pattern), INSM1, Merkel Cell Polyomavirus-Antibody, and negative for TTF-1. A final diagnosis of Merkel Cell Carcinoma was made.  

This case highlights the immunophenotyic overlapping of Merkel Cell Carcinoma with hematopoietic neoplasms, and extends awareness of the diagnostic pitfall for this entity, especially in settings of immunosuppression.