MLL gene rearrangements are found in more than 70% of the cases of infant leukemia, both acute lymphoblastic leukemia (ALL) or acute myeloid leukemia (AML), but are less frequent in leukemia from older children. MLL translocations are also found in approximately 10% of adult AML and in a small proportion of patients with therapy-related leukemia. Independently of their association with other high-risk features at presentation, MLL rearrangements are in most cases predictive of poor clinical outcome. In this study, we report the clinical characterization and frequency and type of MLL rearrangements present in a consecutive series of 45 patients that were diagnosed with acute leukemia in the Portuguese Oncology Institute, Porto, Portugal, over the last 13 years (1998–2011).
Conventional cytogenetic, fluorescence in situ hybridization (FISH), and molecular genetic studies (RT-PCR and LDI-PCR) were used to characterize the type and frequency of MLL rearrangements in a consecutive series of 45 Portuguese patients with MLL-related leukemia treated in a single institution between 1998 and 2011. Additionally, a detailed patient clinical characterization was also performed and statistical analysis using the Kaplan-Meier method as used to evaluate patient survival.
In 43 patients (96% of the cases) we could identify the fusion partner, the most common being the MLLT3, AFF1, MLLT1, MLLT10, ELL, and MLLT4 genes, accounting for 88% of all cases. In the group of patients with acute lymphoblastic leukemia and an identified MLL fusion partner, 47% showed the presence of an MLL-AFF1 fusion, as a result of a t(4;11). In the remaining cases, a MLL-MLLT3 (27%), a MLL-MLLT1 (20%), or MLL-MLLT4 (7%) rearrangement was found. The most frequent rearrangement found in patients with acute myeloblastic leukemia was the MLL-MLLT3 fusion (42%), followed by MLL-MLLT10 (23%), MLL-MLLT1 (8%), MLL-ELL (8%), MLL-MLLT4 (4%), and MLL-MLLT11 (4%). In three patients, fusions involving MLL and a septin family gene (SEPT2, SEPT6, and SEPT9), were identified. The most frequently identified chromosomal rearrangements were reciprocal translocations, but insertions and deletions, some cryptic, were also observed. In our series, patients with MLL rearrangements were shown to have a poor prognosis, regardless of leukemia subtype and treatment protocol. However, patients that received a bone marrow transplant had a better survival than patients that received chemotherapy alone. Interestingly, children with 1 year or less showed a statistically significant better overall survival when compared with both older children and adults.
The use of a combined strategy in the initial genetic evaluation of acute leukemia patients allowed us to characterize the pattern of MLL rearrangements in our institution, including our previous discovery of two novel MLL fusion partners, the SEPT2 and CT45A2 genes, and a very rare MLL-MLLT4 fusion variant.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.