Orbital alveolar soft part sarcoma: case report and literature review Alveolar soft part sarcoma (ASPS) is a malignant soft part tissue tumour of uncertain phenotypic expression that mainly affects young adults and children and represents less than 1% of all sarcomas. 1À4 There are only 63 cases of primary orbital ASPS reported in the PUBMED, none from Canada, with a female preponderance and a predilection for affecting the left eye. 1À3 Herein we describe an unusual case of orbital ASPS primary of the orbit in a 31-year-old female with a previous history of breast cancer.A 31-year-old female presented a mild proptosis of the right eye. After magnetic resonance imaging (MRI), the preliminary diagnosis was a metastasis of her previous breast carcinoma. At age 26 years, she was diagnosed with a grade 3 invasive ductal carcinoma of the right breast, stage T2 N2.Genetic screenings were negative.The first MRI showed a solitary lesion in the right orbit measuring 16 £ 15 £ 14 mm. The location was intramuscular inferior right, and the lesion was well circumscribed and reconfigured the orbit's floor. It caused swelling of the superior right portion of the optic nerve. It was iso-intense T2 and T1 with an enhanced homogeny after gadolinium injection.Two months later, a second MRI showed an increase in size of the lesion, measuring 18 £ 18 £ 17 mm (Fig. 1A). Biopsy demonstrated a tumour composed of uniform polygonal epithelioid cells in a solid and alveolar architecture outlined by delicate sinusoidal vascular channels. The cells had abundant granular eosinophilic cytoplasm and vesicular nuclei with large prominent nucleoli and a very low mitotic rate with no necrosis (Fig. 1C and D). Periodic acidÀSchiff with diastase stains revealed needle-shaped crystals (Fig. 1E). Immunohistochemical stains performed demonstrated tumour strong positivity for Fig. 1-A, CT scan of the orbit showed a well-circumscribed lesion in the right orbit. B, Microscopic examination shows a monotonous and uniform tumour with a sinusoidal architecture (hematoxylin-eosin [H&E], 20 £). C, The tumour is composed of monomorphic cells with vesicular nuclei and a central nucleoli, eosinophilic and granular cytoplasm, with rare cellular pleomorphism and rare mitotic figures (H&E, 400 £). D, Vascular invasion was identified at the periphery of the tumor (H&E, 40 £). E, Needle-shaped crystals were identified in the cytoplasm of some of the tumoural cells by periodic acid-Schiff (PAS) with diastase stain (PAS diastase, 400 £). F, The tumoural cells show a diffuse nuclear positivity for TFE3 by immunohistochemistry (TFE3, 100 £).