Proximal-type epithelioid sarcoma of the vulva with INI1 diagnostic utility

Proximal epithelioid sarcoma (PES) is an extremely uncommon neoplasm of the vulva with an aggressive behavior. Recently, these authors experienced a case of proximal-type ES in a 41-year-old woman who was admitted for a rapidly growing mass in the right mons pubis. An about-1-cm-sized mass was initially noticed one and a half years earlier. The excised mass, however, was 8 cm in greatest dimension and was relatively well circumscribed. The cut surface was trabeculated, with multifocal hemorrhages and necroses. Microscopically, the tumor consisted of epithelioid rhabdoid cells with vesicular nuclei, large prominent nucleoli, and cytoplasmic eosinophilic globules comparted by thin, fibrous septae. The main differential diagnoses included PES, other sarcomas with epithelioid cells, malignant melanoma, and sarcomatoid carcinoma. The tumor cells were diffusely positive for vimentin and EMA; focally positive for cytokeratin; and negative for CK5/6, CD34, S-100 protein, desmin, and myogenin. INI1 (hSNF5/SMARCB1, a member of the SW1/SNF chromatin remodeling complex located on chromosome 22q11.2) staining clearly showed loss of expression in the tumor cells. Recent studies reported that some ESs also showed INI1 inactivation, as characteristically seen in malignant rhabdoid tumors of infancy. Reported herein is the diagnostic utility of INI-1 on PES and the possible relationship between PES and malignant rhabdoid tumor of the soft tissue, besides a collective review of the reported cases of PES of the vulva and of the current case.