Gradual darkening of the skin is a clinical symptom of cutaneous malignant melanoma. Malignant melanoma of skin (MM) is a malignant tumor that originates from normal melanocytes or original nevus cells in the epidermis. Although it is less common than skin cancer, it is highly malignant, progresses rapidly, is dangerous and has a very poor prognosis. Then, what tests are needed for the gradual darkening of skin? The following are the examinations that need to be done for the gradual darkening of skin. 1, urine examination: when there is a large amount of melaninogen and its metabolites in the urine and black urine, it is helpful to confirm the diagnosis of melanoma. X-ray, B-ultrasound, CT, MRI and radionuclide scan are helpful to determine whether melanoma has metastasis in lung, liver, kidney, brain and other internal organs. Histopathological examination: abnormal proliferation of melanocytes can be seen, with nests of cells in the epidermis or at the epidermal-dermal boundary. The nuclei are usually eosinophilic and “bird’s eye” like. In aggressive melanoma, melanoma cells can be seen in the dermis or subcutaneous tissue. For typical melanoma, pathological examination of HE-stained sections is usually sufficient to make a definitive diagnosis. However, atypical melanomas, such as anaplastic melanoma, often require special techniques (e.g., S-100 and HMB-45 immunohistochemistry) to aid in the diagnosis.