How does a skin doctor determine whether a mole is benign or malignant?

Pigmented lesions: Key features that suggest a need for excision or biopsy of a pigmented lesion are 1)irregular vs. smooth margins, 2) variation in pigmentation; 3) any asymmetry; and 4) change in appearance/ or size. The appearance is only one key factor however. The patient history or family history, amountof sun damage and other factors may also influence the urgency for biopsy.