Abstract
T-lymphoblastic leukemia/lymphoma (T-ALL/LBL) accounts for approximately 15% of pediatric and 25% of adult ALL, and KMT2A(MLL) gene rearrangements are observed in approximately 4% to 8% of T-ALL/LBL cases. To date, a scarcity of literature is available for KMT2A rearrangements in pediatric T-ALL/LBL. Following a 10-year review of cytogenetic data, we report our experience with KMT2A rearrangements observed in pediatric T-ALL/LBL. An IRB-approved, 10-year retrospective review of the Mayo Clinic cytogenetic databases was performed to identify KMT2A rearrangements in specimens sent for T-ALL/LBL FISH studies in patients under the age of 30 years. Of 806 total studies performed on unique individuals, 32 harbored KMT2A rearrangements. Four of the 32 cases were excluded due to an exclusionary diagnosis or nonspecific reason for referral, resulting in a total of 28 cases. Twenty-five of 28 patients (89.3%) were referred for T-ALL and 3 patients were referred for T-LBL (10.7%). Eighteen patients were male and 10 were female (M:F ratio, 1.8:1) with ages ranging from 1 to 20 years (mean 12, median 12). Specimen types included bone marrow (n = 21), blood (n = 4), and tissue (mediastinal mass [n = 2], supraclavicular lymph node [n = 1]). Of the 28 cases, 9 (32.1%) had a KMT2A/MLLT1 fusion, 8 (28.6%) had an AFDN/KMT2A fusion, 2 (7.1%) had a KMT2A/ELL fusion, and 1 (3.6%) had a MLLT10/KMT2A fusion. In addition, five cases (17.9%) had KMT2A rearrangements with unidentified gene fusion partners and three cases (10.7%) had partial KMT2A deletions. No AFF1/KMT2A or MLLT3/KMT2A fusions were observed. In our retrospective study, KMT2A gene fusion partners observed in pediatric T-ALL/LBL most commonly involved MLLT1 or AFDN (17 of 28 cases). Interestingly, no AFF1/KMT2A or MLLT3/KMT2A fusions were observed. These results may indicate an age-related association between KMT2A rearrangements and fusion partner genes.
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