The gradual darkening of the skin is a clinical symptom of cutaneous malignant melanoma. Although it is less common than skin cancer, it is highly malignant, rapidly progressing, sinister and has a very poor prognosis. Then, how to diagnose the gradual darkening of the skin? The following are the diagnostic methods for the gradual darkening of skin. 1, histopathological examination: abnormal proliferation of melanocytes can be seen, and there are cell nests 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, for atypical melanoma, such as anaplastic melanoma, some special techniques (such as S-100 and HMB-45 immunohistochemical examination) are often required to help the diagnosis. 2.Urinal examination: When a large amount of melaninogen and its metabolites appear in urine with black urine, it is helpful to confirm the diagnosis of melanoma. X-rays, ultrasound, CT, MRI and radionuclide scan are helpful to determine whether melanoma has metastasis in lung, liver, kidney, brain and other internal organs.