A Case of Rare Adipocytic Tumor of the Tongue: Lipoblastoma-Like Tumor With RB1 Gene Deletion.

Lipoblastoma-like tumors (LLTs) are benign adipocytic tumors characterized by an admixture of lipoblasts within the myxoid stroma, primarily affecting the vulvovaginal area in young patients. Rare cases have been reported in other locations, including the orofacial region. Here, we present a unique case of LLT of the tongue in a 62-year-old woman with a slowly developing painless nodule. The tumor showed no signs of recurrence five years after surgery. Histopathological examination revealed a myxo-fatty lobulated lesion with numerous uni- and multi-vacuolated lipoblasts and prominent chicken-wire capillaries. Immunohistochemistry showed positivity for S100, whereas the tumor was negative for cluster of differentiation 34 (CD34), pleomorphic adenoma gene 1 (PLAG1), B-cell lymphoma 2 (BCL-2), mouse double minute 2 homolog (MDM2), cyclin-dependent kinase 4 (CDK4), and DNA damage-inducible transcript 3 (DDIT3). The retinoblastoma protein (pRB) was partially negative and exhibited mosaic patterns. Fluorescence in situ hybridization (FISH) analysis indicated a hemizygous deletion of the RB1 locus in 36% of tumor cells, with no MDM2 amplification detected. This case highlights the diagnostic challenges of differentiating LLTs from spindle cell lipomas (SCLs), particularly in the context of pRB deficiency and RB1 deletion. This case exemplifies the molecular heterogeneity of neoplasms with lipoblastoma-like features.