Deep Cavernosal Melanoma Without Clinically Evident Mucosal or Cutaneous Involvement: A Case Report

Penile melanoma is an extremely rare malignancy, representing less than 0.1% of all melanomas. It most commonly arises from the glans, foreskin, or urethral meatus. Deep cavernosal involvement without clinically evident cutaneous, mucosal, or urethral disease is an unusual presentation and poses significant diagnostic and therapeutic challenges.

A 23-year-old male presented with progressive penile induration and pain. MRI revealed a lesion predominantly involving the corpus cavernosum, with no clinically evident cutaneous, mucosal, or urethral involvement. An excisional biopsy established the diagnosis of malignant melanoma; however, the initial specimen showed tumor involvement of the resection margin and did not include epidermal sampling. Systemic staging with whole-body CT and PET-CT showed no evidence of metastatic disease. The patient subsequently underwent partial penectomy with bilateral sentinel lymph node dissection, showing negative sentinel lymph nodes and free final surgical margins. One year later, 18F-FDG PET-CT demonstrated nodal and osseous metastatic disease, with hypermetabolic lymphadenopathies in the distal retroperitoneal, left iliac, and left inguinal regions, osseous lesions in the sternal manubrium, and a new right upper-lobe pulmonary micronodule. The patient received immunotherapy with a limited clinical response.

This case describes an unusual presentation of melanoma predominantly involving the corpus cavernosum without clinically evident cutaneous, mucosal, or urethral involvement. The absence of epidermal sampling prevents definitive histological exclusion of a regressed or deeply invasive mucosal/cutaneous primary lesion. This report highlights the aggressive behavior of deeply located penile melanoma and the need for careful clinicopathological correlation and individualized multidisciplinary management.