Solitary fibrous tumor of deep parotid gland preoperatively classified as salivary gland neoplasm of uncertain malignant potential by the Milan system for reporting salivary gland cytopathology: A common diagnosis for a rare entity.

Abstract

Solitary fibrous tumor (SFT) is a rare fibroblastic tumor with spindle cell morphology, which is characterized by a prominent branching vasculature and a NAB2-STAT6 gene rearrangement. SFT may occur in any anatomical site and may involve salivary glands, including the parotid gland. We present a young female with a primary parotid SFT diagnosed as "neoplasm-Salivary gland neoplasm of uncertain malignant potential (SUMP)" per the Milan system for reporting salivary gland cytopathology by fine-needle aspiration (FNA) with surgical pathology follow-up. Cytomorphology of SFT is diverse and overlaps with more common entities causing a diagnostic challenge. Non-diagnostic FNA results are not uncommon. Thankfully, the majority of SFTs involving the salivary gland can be identified as "neoplasm" on FNA. The Neoplasm-SUMP subcategory is considered for the majority of cases, which would warrant a diagnostic excision with clear surgical margins, which is also curative in most cases. The Neoplasm-SUMP also perfectly encompasses the neoplastic behavior of SFT, which runs on a scale from indolent to malignant.