Spontaneous regression of aleukemic leukemia cutis harboring a NPM/RARA fusion gene in an infant with cutaneous mastocytosis.

Aleukemic leukemia cutis has been rarely reported in infant leukemia. This report describes a 6-month-old boy with aleukemic leukemia cutis, which regressed without any treatments within 6 months. Interestingly, a cytogenetic analysis disclosed a leukemia clone with the karyotype of 46, XY, t(5;17)(q35;q12), which generated nucleophosmin (NPM)-retinoic acid receptor alpha fusion (RARA) fusion transcripts. The patient simultaneously had cutaneous mastocytosis, which also disappeared with the leukemia cutis. He shows no physical or laboratory abnormalities without any treatments after 12 months, although the NPM/RARA transcripts remain faintly in the bone marrow. The present case is partially compatible with systemic mastocytosis with an associated clonal hematologic non-mast cell lineage disorder, proposed by the WHO classification, and it is also suggestive of the initiation or early stage of acute promyelocytic leukemia.