Acute promyelocytic leukemia diagnosed on soft tissue biopsy: a rare extramedullary presentation Free

A 20-year-old woman presented with myeloid sarcoma on clavicular mass biopsy. Magnetic resonance imaging confirmed a soft tissue mass encasing the clavicle (panel A) and epidural infiltration of the leukemic infiltrate from L4-5 down to the S3 level. Bone marrow biopsy was normal (morphology, immunophenotype, and karyotype). Repeat clavicular mass biopsy was performed for full leukemic workup. Touch preparation from mass (panel B; 100× objective cropped) demonstrated many bilobed blasts and blasts containing Auer rods, consistent with acute promyelocytic leukemia (APL). Hematoxylin and eosin stain showed binucleate cells (panel C; 100× objective) and myeloperoxidase (MPO) immunohistochemistry confirmed myeloid lineage (panel D; 100× objective). The immunophenotype (positive for CD13, CD15, CD33, CD64, CD38, CD56, and MPO; variable for CD34, HLA-DR, CD117 and CD123; and negative for other lineage defining markers), G-banding karyotype (47,XX,+8,t(15;17)(q24;q21)[7]/46,XX[23]), fluorescence in situ hybridization (FISH) for PML::RARA (dual-fusion signal pattern detected), and positive PML::RARA transcripts by RT-PCR, confirmed APL. Gene panel sequencing identified FLT3-ITD (VAF 27%) and GATA2 (17%) mutations. Retrospective testing was performed on the staging bone marrow: FISH for PML::RARA was negative; however, RT-PCR for PML::RARA was positive.

This case highlights a rare presentation of APL as myeloid sarcoma, without peripheral blood or morphological marrow involvement. Myeloid sarcomas occur in 3% to 5% of APL cases, usually at relapse. De novo presentation in soft tissue without marrow involvement is very rare.

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