RESUMEN
BACKGROUND: Congenital acute nonlymphoblastic leukemia (cANLL) is an extremely rare event and represents only 0.5-1% of the leukemias in the first year of life. It is usually more common among patients with chromosomal abnormalities. Transient myeloproliferative disease (TMD) is an hyperleukocytosis entity that occurs almost exclusively in Down syndrome patients and remits spontaneously. Spontaneous remission of congenital leukemia has been reported and related to the presence of an extra chromosome 21. PROCEDURE: A pair of non-Down syndrome newborn twins presented with a clinical picture of skin rash and hyperleukocytosis. Twin B had full-blown cANLL with bone marrow, peripheral blood, skin, CSF, and placental invasion. Twin A presented transient peripheral blood and skin involvement by the same type of blast cells. No cytotoxic therapy was given. With 2 years follow-up, they continue to do well. RESULTS: Histologic and immunophenotypical analysis of placentas, cord blood, skin, CSF, bone marrows, and peripheral blood revealed a consistent picture of intrautero cANLL in twin B, with transplacental invasion of twin A. Normal and blast cells were found to be karyotypically normal. Spontaneous remission occurred. CONCLUSIONS: cANLL with karyotypically normal blasts can develop a self-limited clinical course, which has resemblances to TMD.