Cutaneous Malignant Rhabdoid Tumor in the Palm of an Adult
A 27-year-old male consulted our Medical Center complaining of a right palm neoplasm that had been present for 6 months. On examination, a 4.0×4.5 cm, hard, round, protuberant tumor was found on the ulnar side of the right palm (). Magnetic resonance imaging (MRI) showed that the mass adhered to the 5th metacarpal bone and invaded the hypothenar muscle and flexor tendons, but no mass in the head and abdomen. Histological analysis of a biopsy specimen suggested epithelioid sarcoma. Computed tomography revealed right axillary lymph node metastasis.\nSurgery consisted of radical excision of the palm tumor along with axillary lymph node resection. En bloc resection of the tumor with a skin margin of 2 cm, including the 5th metacarpal bone, 4th intrinsic muscles, 5th flexor tendons, and neuro-vascular bundle, was performed. The 4th metacarpal bone-exposing wound was covered with artificial dermis.\nAfter verification that the surgical margins were free from tumor invasion by histological analysis, secondary reconstruction with the nerve graft and free skin graft was performed 2 weeks later. The patient received 4 chemotherapies with doxorubicin (30 mg) and ifosfamide (5 g), and radiotherapies with a total dose of 60 Gy to the palm and axilla.\nAfter 12 months, the patient showed no tumor relapse, and regained pinch and grip function and showed resolved sensory disturbance of the ring finger.\nMacroscopically, the tumor was located in the subcutis, measuring approximately 4.0×4.5 cm in size. It was grossly recognized by its white-yellow color with poor delimitation between the tumor and surrounding soft tissue. Microscopically, the sections showed the proliferation of round or oval tumor cells with vesicular rounded nuclei, prominent nucleoli, and eosinophilic cytoplasm in a sheet, accompanied by a focal myxoid matrix. Abundant rhabdoid cells with cytoplasmic inclusion bodies were observed (). Mitotic figures were occasionally noted. Immunohistochemically, the tumor cells were positive for S-100 protein, GFAP, beta-catenin, and EMA (), but negative for cytokeratins (CAM5.2, AE1/AE3, CK 14), alpha-SMA, desmin, HHF35, p63, HMB45, Melan A, MiTF, CD34, HLIB45, glypican 3, and myogenin. The loss of SMARCB1 (SWItch/Sucrose NonFermentable-related, matrix-associated, actin-dependent regulator of chromatin, subfamily b, number 1)/INI1 immunoreactivity was also recognized. The feature was that of an SMARCB1/INI1-deficient tumor, highly suggestive of an extrarenal malignant rhabdoid tumor.