Unusual presentation of myeloid sarcoma in a case of acute promyelocytic leukemia with a cryptic PML-RARA rearrangement involving multiple sites including the atrium.

Myeloid sarcoma is an extramedullary tumor mass composed of immature myeloid cells. Myeloid sarcoma may develop de novo, concurrently with acute myeloid leukemia (AML), or at relapse. Although myeloid sarcoma can occur at any site, myeloid sarcoma involving the heart is extremely rare. Reported here is the case of a 30-year-old man, initially diagnosed with acute promyelocytic leukemia (APL) in bone marrow, who presented later with myeloid sarcoma at multiple anatomical sites (left scapula, thoracic vertebra, right atrium, and supraclavicular mass) in multiple relapses. Conventional cytogenetic studies performed on the atrial sample revealed a karyotype with additional material on the short arm of chromosome 7, at 7p22. Fluorescence in situ hybridization studies confirmed a cryptic PML-RARA fusion on the short arm of chromosome 7, as well as a second fusion on one copy of chromosome 15. With the fourth and latest relapse, molecular cytogenetic studies performed on interphase nuclei of the myeloid sarcoma specimen (a supraclavicular mass) showed evidence of six related abnormal clones with a PML-RARA fusion, suggesting clonal evolution. This represents a rare case of APL with a cryptic PML-RARA rearrangement presenting as myeloid sarcoma at multiple relapses and involving multiple anatomical sites, including cardiac atrium.