A Rare Case of Myxoid Solitary Fibrous Tumor of the Upper Lip: The Key Role of STAT6 in Diagnosis.

A solitary fibrous tumor (SFT) is an uncommon spindle cell mesenchymal neoplasm that most commonly arises in the pleura. SFTs have been shown to arise in various internal organs but are not typically discovered cutaneously. The diagnosis of SFT requires an integrated approach since SFT can mimic a variety of benign and malignant tumors, both clinically and histologically. To further complicate the histological diagnosis, there are different morphological variants of SFT. Therefore, immunohistochemical markers such as signal transducer and activator of transcription 6 (STAT6) can be utilized for SFT diagnosis due to their high specificity and sensitivity, as nuclear expression of STAT6 is a distinguishing feature of SFT and helps differentiate it from histological mimickers. A correct diagnosis is imperative for proper treatment and management. In this report, we present a 74-year-old healthy man with a growing painless mass on his upper lip for several years. Biopsy results confirmed the diagnosis of SFT with myxoid variation, and the patient underwent a successful excision of the lesion. Our case emphasizes the importance of a multidisciplinary approach and the utilization of immunohistochemical staining when diagnosing superficial tumors.