We know that the vast majority of the moles are basically benign. The American Academy of dermatology expert and specialist dermatologist estimated more than 62,000 new cases of melanoma is been diagnose every year in the USA alone.
The data about the transformation of mole into melanoma is rather controversial. It does appear that 10% of malignant melanoma have a precursor or pre-existing lesion, and of this only 10% are due to melanocytic nevi. The inference is that, the malignant melanoma seldom (1% of all cases) has a melanocytic nevi as a precursor or pre-existing mole lesion. In other words, the melanoma is NOT caused by pre-existing mole but from a new lesion that arise separately from the surrounding skin. This is a consolation for us to NOT to worry that melanoma is NOT significantly arising from the pre-existing mole.