Lipoblastoma in one adult and 35 pediatric patients: Retrospective analysis of 36 cases

Lipoblastoma is a rare benign mesenchymal neoplasm that typically occurs at various sites in infants and children but may also occur in adults. Thus, differential diagnoses are often performed. To understand this tumor type, the present study described clinicopathological features, diagnosis and differential diagnosis of different morphological lipoblastomas. A single-institution retrospective review of 36 lipoblastoma cases diagnosed between 2015 and 2021 was performed. Formalin-fixed paraffin-embedded tissue was used for S-100, CD34, P16 and desmin immunohistochemistry analysis, along with rapid fluorescence in situ hybridization (FISH) detection with pleiomorphic adenoma gene 1 (PLAG1). The 36 cases included 14 females and 22 males [age range, 7 days to 33 years (median, 16.5 years); 28 patients were aged ≤3 years] and the tumors were located in the trunk (n=16), limbs (n=12), head and neck (n=6), and perineum (n=2). Histologically, lipoblastomas were divided into classic (n=15), lipoma-like (n=13) and myxoid (n=8) subtypes. They comprised lobules of mature adipose tissue of varying size and a fine capillary network surrounded by mucinous stroma. Single- or multivesicular lipoblasts positive for S-100 (29/36, 81%) were observed, with occasional mature adipocytes. Peripheral vessels and cytoplasm of primitive mesenchymal cells were diffusely positive for CD34 (36/36, 100%), whereas primitive mesenchymal cells and striated muscle tissue were positive for desmin (26/36, 72%). Most tumor cells were negative while only few were positive for P16 (8/36, 22%). FISH revealed PLAG1 breakage and rearrangement in 24/32 (75%) patients. In total, 28 patients were followed up post-operatively (range, 2-84 months; median, 41 months; 3 patients relapsed and 8 were lost to follow-up). In conclusion, diagnosis of a typical lipoblastoma is not difficult and PLAG1 breakage detection is key for the diagnosis.