Atypical nevus is the pre-melanoma

Mild Atypical nevus on the thigh.

Atypical nevus is a pre-melanoma neoplasm. It is benign, until it continues to grow and eventually become a melanoma, then it is a deadly cancer.  It starts as a freckle on your skin. Then it starts to change from a brown freckle to having brown and black, irregular borders, irregular shape. It starts to change over months. The atypical nevus is first mild, then moderate, and finally severe. At some point it becomes melanoma in-situ. 

All people receive radiation damage to their skin. Some people are more able to deal with the damage (ie, some people have a healthier immune system). The quicker your skin pushes off the top layer of cells, the easier it is for the body to remove the damage. If the body does not eliminate the damaged cells, the area becomes an atypical nevus. That region continues to grow and change. Then it becomes a deadly cancer.

The best strategy is to see a dermatologist, get full body skin checks and have these neoplasms removed before they grow into cancer.