Cytomorphological Spectrum of Solitary Fibrous Tumor: Revisited

Cytological Perspective in a Case of Doege-Potter Syndrome With Hypoinsulinemic Hypoglycemia

Solitary fibrous tumor (SFT) of the lung is a rare mesenchymal neoplasm of uncertain histogenesis, unknown molecular features, and unpredictable clinical behavior, characterized by NAB2-STAT6 fusion. Hypoglycemia accompanying SFT (Doege-Potter syndrome) is an uncommon presentation. We present the cytomorphological features on biopsy imprint smears of a histopathologically confirmed case of SFT of the lung with an uncommon presentation. A 76-year-old non-smoker, non-alcoholic, and non-diabetic man presented with complaints of intermittent episodes of confusion with syncopal attacks (>10 episodes) for six months. The patient had no respiratory complaints and no history of weight loss. Laboratory investigations revealed fasting blood sugar of 38 mg/dl with low serum insulin and C-peptide levels. Physical examination revealed reduced air entry on the left side of the chest. Chest X-ray showed left-sided homogenous opacity. High-resolution computed tomography (HRCT) of the chest showed a large left-sided lung mass. A biopsy was performed. Biopsy imprint smears were cellular and showed tumor cells arranged in clusters and fragments with traversing capillaries displaying monomorphic pump to oval nuclei, fine granular evenly dispersed chromatin, regular nuclear membrane, inconspicuous nucleoli, and a moderate amount of wispy cytoplasm. Foci of intercellular hyaline stromal material were noted. A cytodiagnosis of low-grade mesenchymal neoplasm was made. Histopathology revealed a cellular tumor comprising tightly packed round to fusiform cells arranged around blood vessels with intervening thick collagen, positive for CD99, vimentin, BCL2, CD34, and STAT6 and negative for EMA, CK AE1/AE3, S100, TLE1, and SMA. Familiarity with cytomorphology plays a pivotal role in clinching an early diagnosis of this rare neoplasm of the lung, particularly in the setting of presentation with hypoglycemia.

Pitfalls in soft tissue cytopathology

Fine needle aspiration biopsy (FNAB) is a diagnostic modality for the evaluation of suspicious soft tissue masses. Despite its reasonable sensitivity, specificity and positive predictive value in differentiating benign from malignant neoplasms, the exact subtyping of the primary soft tissue tumours can be challenging. Certain tumours constitute "pitfalls" and add to the diagnostic challenge. This review provides a detailed account of the diagnostic challenges in soft tissue cytopathology, including pitfalls and, more importantly, the ways to overcome these challenges by integrating clinical details, key cytomorphological features and judicious application of ancillary techniques.

Metastasis of solitary fibrous tumor to the parotid gland diagnosed on aspiration cytology supplemented with immunocytochemistry

Solitary fibrous tumor (SFT) can occur in varied anatomic locations, most commonly being the extremities-superficial and deep soft tissues, followed by retroperitoneum, visceral organs, and the bone. Head and neck region may harbor a few with a predilection for the orbit and sinonasal tract, oral cavity, and rarely the salivary glands. The parotid gland is most involved among all salivary glands. Overall, SFT in salivary glands is rare and mostly seen as a primary tumor. The occurrence of metastasis to the parotid gland is exceedingly uncommon. We present cytological findings of SFT, metastatic to the parotid gland in a young 31-year-old lady where the diagnosis was confirmed with the help of immunocytochemistry (ICC) on the cell block. The smears were highly cellular and showed predominantly discrete round to oval tumor cells with mild pleomorphism, coarse chromatin, inconspicuous nucleoli, and scanty cytoplasm. Mitosis and focal areas of necrosis were noted. Lymphoglandular bodies were absent ruling out a non-Hodgkin lymphoma. Features were of a poorly differentiated malignant tumor with differentials being sarcoma, myoepithelial carcinoma, and carcinoma ex-pleomorphic adenoma. A panel of ICC was done and positivity for signal transducer and activator of transcription 6 (STAT6) helped in clinching the correct diagnosis of SFT.