Fig. 1

Morphological features of case 1. a The surgical specimen’s cut surface reveals a whitish-brown tumor bulging towards the urethra. The red arrowhead indicates the resection line of the urethra, while the black asterisk identifies the corpus cavernosum. b This low-magnification image demonstrates a highly cellular tumor originating from the surface of the glans and invading the surrounding structures (H&E stain, 70x). c The tumor is composed of anaplastic epithelioid and spindle cells. Additionally, brown intracytoplasmic pigment is present, and bizarre tumor cells can be occasionally observed (H&E stain, 200x). The inset reveals diffuse positivity of tumor cells with SOX-10 (SOX-10 immunohistochemistry, 200x). d Brisk mitotic activity with atypical cell divisions is evident [yellow arrowhead] (H&E stain, 400x). The inset presents Ki-67-positive cells with 80% positivity in the hot-spot areas (Ki-67 immunohistochemistry, 200x). e Below the non-keratinizing squamous epithelium of the glans, an in situ component and pagetoid spread is observed (H&E stain, 200x). The tumor cells display diffuse PRAME expression (PRAME immunohistochemistry, 100x).