Cutaneous malignant melanoma of the breast is a rare tumor, accounting for less than 5% of all malignant melanomas, Surgical resection is the commonly adopted treatment method for malignant melanoma, supplemented by chemotherapy, radiotherapy, and immunotherapy treatments, resulting in a comprehensive treatment strategy. We aim to assess the efficacy of adjuvant radiotherapy in managing cutaneous malignant melanoma of the breast in long-term local and regional control.

A 65-year-old Libyan woman was diagnosed with stage III primary cutaneous malignant melanoma of the breast in 2021. She presented with a progressive painless mass of preexisting nevus, which is located on the skin of the upper inner quadrant of her left breast post-wide local excision without ipsilateral regional lymph node sampling. A month later, a regional ipsilateral axillary LN recurrence occurred. Modified radical mastectomy and axillary LN dissection were done.

subsequently, six cycles of chemotherapy were received, followed by 40 GY in 15 fractions of adjuvant radiotherapy to the left chest wall, ipsilateral axilla, and supraclavicular LNs. In November 2022, lung metastasis was identified, and immunotherapy was advised, Subsequent imaging up to January 2024 indicated no local or regional recurrences and a complete disappearance of lung metastasis.

The rarity of cutaneous malignant melanomas of the breast has made it difficult to evaluate a life-threatening disease in which local recurrence and regional or distant metastasis may develop after surgical removal of MM, which is common. Wide local excision and prophylactic lymphadenectomy, including radical mastectomy, gave the best long-term local and regional control. Internal mammary node Dissections are not indicated; radiotherapy decreases locoregional failure from 30-50 % to 10–20%.

Given the notable local, regional recurrence, and distal metastasis rate, local radiotherapy and immune checkpoint inhibitors monotherapy could serve as potent adjuvant treatment in metastatic cutaneous breast malignant melanoma.