Pediatric and Adult Sinonasal Phosphaturic Mesenchymal Tumors: CDKN2A Copy Number Alterations and Their Association with Recurrence.

PURPOSE: Phosphaturic mesenchymal tumors (PMTs) are exceptionally rare neoplasms that secrete fibroblast growth factor 23 (FGF23), leading to tumor-induced osteomalacia (TIO). Owing to their nonspecific clinical manifestations and deceptively bland morphology, diagnosis is frequently delayed unless there is a high index of clinical suspicion or recognition of characteristic histopathological features. While PMTs predominantly arise in the appendicular skeleton, involvement of the sinonasal tract is uncommon, and pediatric sinonasal PMTs have not been reported previously. Although most PMTs follow a benign course, a subset demonstrates local recurrence, and predictors of recurrence remain poorly defined.

METHODS AND MATERIALS: All cases of sinonasal PMTs diagnosed at our institution over a 10-year period were retrospectively reviewed. Clinical, radiological, histopathological, immunohistochemical, and molecular findings were analyzed. Immunohistochemistry was performed for SATB2, ERG, SMA, CD56, desmin, SSTR2, SSTR5, FGFR1, and Ki-67. Fluorescence in situ hybridization (FISH) was performed using FGFR1 dual-color break-apart and CDKN2A/CEP9 dual-color locus-specific probes.

RESULTS: Seven sinonasal PMTs were identified, including two pediatric cases (both 10-year-old females) and five adult cases (age range: 32-68 years; overall range: 10-68 years). Patients presented with non-specific symptoms, most commonly related to tumor-induced osteomalacia, while a minority presented with local sinonasal complaints. Histologically, all tumors were unencapsulated and composed of ovoid cells embedded within a characteristic pale eosinophilic stroma with prominent, often dilated vasculature. Adipose tissue was present in 6/7 (85.7%) cases, osteoclast-like giant cells and hemosiderin-laden macrophages in 4/7 (57.1%) each, whereas grungy calcification, osteoid-like matrix, and aneurysmal bone cyst-like areas were infrequent. Tumors showed diffuse expression of SATB2, ERG, SMA, CD56, and SSTR2, while FGFR1 immunohistochemistry lacked specificity. FGFR1 gene rearrangement was identified by FISH in two cases. Notably, both pediatric tumors demonstrated CDKN2A homozygous deletion and developed local recurrence, whereas none of the adult tumors showed CDKN2A loss or recurred.

CONCLUSION: Sinonasal PMTs are rare neoplasms that pose significant diagnostic challenges because of their rarity and morphological overlap with other mesenchymal tumors. Recognition of their characteristic histological features, supported by an appropriate immunohistochemical panel and FGFR1 FISH, facilitates accurate diagnosis. This study represents the first report of pediatric sinonasal PMTs and identifies CDKN2A homozygous deletion as a potential marker of recurrent behavior, warranting further investigation in larger cohorts.