Generally speaking, the chance of cancerous transformation of an acquired pigmented nevus is extremely low. According to statistics, about 80% of malignant melanomas occur on skin or mucous membranes without any prior pigmented nevi, and only 20% are carcinomas based on pre-existing pigmented nevi. Most of these pigmented nevi are dysplastic nevi. They are clinically evaluated according to the ABCD criteria: (1) asymmetrical shape (A), (2) irregular margins (B), (3) mottled color (C), and (4) diameter greater than 6 mm (D). Any lesion with the above two items is called clinically atypical nevus and should be removed for pathological examination. In addition, giant congenital pigmented nevi are more likely to develop cancer. In view of the fact that malignant melanoma is rare in China, and most of the pigmented nevi in these areas are junctional nevi, therefore, when pigmented nevi in palmoplantar and nail mother suddenly increase in size within a short period of time, with irregular edges, uneven pigmentation, or even ulceration and bleeding, you should go to a regular hospital and have pathological examination as soon as possible to avoid delaying the disease.