Rearrangements of the MLL gene located at chromosome 11q23 are common chromosomal abnormalities associated with acute leukemias. In vast majority of cases with MLL gene rearrangements, only one chromosome 11 or a single MLL allele got involved. We report two very unusual cases of myeloid neoplasms with homozygous inv(11)(q21q23) and biallelic MLL rearrangement. Both patients, a 12-year old boy and a 29-year old woman, presented initially with T lymphoblastic leukemia/lymphoma (T-ALL), achieved complete remission with intensive chemotherapy, then recurred as acute myeloid leukemia in one patient and therapy-related myelodysplastic syndromes in the other patient, 24 and 15 months after initial T-ALL diagnosis, respectively. In both cases, biallelic MLL gene rearrangements were confirmed by fluorescence in situ hybridization. Mastermind like 2 gene was identified as MLL partner gene in one case. To our knowledge, homozygous inv(11)(q21q23) with two MLL genes rearrangement are extremely rare; it is likely a result of acquired uniparental disomy.
Keywords: Inv(11)(q21q23); MLL-MAML2 fusion; T lymphoblastic leukemia; acquired uniparental disomy; homozygosity; myeloid neoplasms.