Malignant melanoma is a kind of highly malignant tumor, which mainly occurs in the skin, mucous membrane, and rarely in the breast. Here we reported a case of malignant melanoma in the chest wall skin with mammary metastasis. A sizable pigment spot on the skin of the thoracic region was found at the patient’s birth, existing for 50 years with quite atypical clinical manifestation. A nodule at 12 o’clock of the left breast was found by ultrasound four months ago, who was mistaken for a fibroadenoma. As a result, the patient received a minimally invasive excision of the breast lesion, after which the pathological report suggested malignant melanoma. By sharing this case, we aimed to discuss the diagnosis and treatment of this kind of atypical malignant melanoma in detail and provide some clinical experience.