Malignant Soft Tissue Tumors of Uncertain Origin. Alveolar soft part sarcoma. A. Grossly, alveolar soft part sarcoma shows a fleshy yellow-gray cut surface. B. Microscopically, the tumor is composed of monotonous densely packed nests separated by thin but richly vascularized septa (hematoxylin and eosin [H&E], 3100). C. The nests contain epithelioid cells with abundant pink cytoplasm (H&E, 3400). D. Cytoplasmic periodic acid–Schiff-positive granules can usually be found (3400). Soft Tissue Tumors of Uncertain Origin. R. Alaggio, C. Coffin, S. Vargas. Published 1 January 2012. Medicine Pediatric and Developmental Pathology. Not Altered. CC.