Novel pediatric aggressive adipose tumor with pathogenic TERT promoter variant and an initial durable response to vincristine and dactinomycin.

Lipoblastomatosis is a rare soft tissue tumor composed of embryonal white fat (1, 2), more common in males <3 years and usually <5cms diameter (1, 2). These benign lesions spontaneously resolve due to gradual maturation, with no reported deaths in childhood (1-4). However, lipoblastomatoses usually require surgical management prior to maturation, due to morbidity related to mass effects (5-7). The aim of surgery is complete resection, with subsequent surveillance for recurrence, which occurs frequently requiring further resection(s) (1, 2, 8-10). There is no proven role for chemotherapy or radiotherapy. Typical histology shows adipocytes with varying maturation, myxoid areas, and vascular networks (1, 10). Immunohistochemistry usually demonstrates S-100, CD56, CD34, and desmin positivity, with p16 negativity (1, 2, 10). Genetic analyses demonstrate structural alteration of chromosome 8q11-13 in 52-75% of cases, resulting in increased expression of oncogenic PLAG1 (1, 2, 11). Alternatively, rearrangement of HMGA2, an upstream activator of PLAG1, may be observed (1, 2). Lipoblastomatoses also commonly have a pseudodiploid or hyperdiploid karyotype and additional copies of chromosome 8 (1-3).