Abstract
Extragastrointestinal stromal tumors (EGISTs) are rare tumors carry the same morphological, immunohistochemical and molecular features as gastrointestinal stromal tumors (GISTs) and involve extragastrointestinal tract soft tissue. Most cases of reported EGISTs arise from soft tissue within the abdomen (mesentery or omentum), retroperitoneum or pelvis. A major subset of such tumors originates from the gastrointestinal musculature, grow in an exophytic manner, and subsequently lose their attachment to the GI tract. Consequently, true EGISTs are exceedingly rare. We report a case of an EGIST (extra-gastrointestinal stromal tumor) involving the vulva. A 77-year-old woman presented with a painless subcutaneous nodule on the right perineum. An excisional biopsy demonstrated a 1.3 cm dermal circumscribed spindle cell lesion. The cells were uniform with faintly eosinophilic cytoplasm and bland elongated nuclei with inconspicuous nucleoli. The mitotic rate was moderately increased. Cytological atypia and necrosis were absent. The tumor cells were positive for CD117 and DOG-1 and negative for smooth-muscle myosin (SMA), STAT6, low and high-molecular weight cytokeratins, SOX10, MART-1, CD10, S-100 protein, estrogen, and progesterone receptors. A diagnosis of EGIST was made and complete excision was recommended. Primary vulvar/perineal EGISTs are extremely rare; only one documented case is described which presented as a recurrent vulvar mass after a diagnosis of leiomyosarcoma was rendered. EGISTs can be misdiagnosed as more common cutaneous/subcutaneous spindle-cell neoplasms, both benign and malignant, including smooth muscle neoplasms (leiomyoma/leiomyosarcoma), spindle cell melanoma, and sarcomatoid squamous cell carcinoma. It is important to correctly diagnose EGISTs and be aware of their unusual locations because of their malignant potential and recent advances in their management with targeted therapy. Metastatic disease should be clinically excluded at unusual sites.
Financial Disclosure:
No current or relevant financial relationships exist.
