Low‐fat and fat‐free spindle cell lipomas in the oral cavity: Immunohistochemical analysis and review of the literature

Abstract

The low‐fat and fat‐free spindle cell lipomas (SCLs) are rare and often mistaken for other benign and malignant morphological mimics, due to the fact that the diagnosis lies on its nonlipogenic component analysis. Here, we report the clinicopathological features of two oral SCLs (low‐fat and fat‐free variants). Both lesions presented clinically as an asymptomatic nodule, which initially yielded diagnostic difficulties on the morphological analysis alone. A case was diagnosed as low‐fat SCL on the lower lip in a 29‐year‐old man, while other as fat‐free SCL on the buccal mucosa in a 46‐year‐old man. In both cases, immunohistochemistry showed strong positivity for CD34 and, remarkably, retinoblastoma (Rb) protein was deficient. Mast cell (MC) tryptase and toluidine blue stain highlighted numerous MCs distributed throughout all tumor stroma. Alpha‐SMA and desmin were negative. S100 evidenced scarce adipocytes only in low‐fat SCL case. Conservative surgical treatment was performed and no recurrence was noticed in about 2‐year of follow‐up in both cases. Due to the potential pitfalls, careful morphological analysis of the tumor stroma in the low‐fat/fat‐free SCL diagnosis, supported by immunohistochemistry (especially CD34, Rb and MC tryptase), is strongly recommended. To the best of our knowledge, this is the first and second case report of fat‐free and low‐fat SCL, respectively, in the oral cavity.