Melenoma either begins de novo or develops from a preexisting lesion, such as a congenital or atypical mole. A classification into several different types was devised after observing that the microscopic either begins de novo or develops from a preexisting lesion, such as a congenital or atypical mole. A classification into several different types was devised after observing that the microscopic Superficial spreading melenoma . SSM is most common in middle age, from the fourth to fifth decade. It develops anywhere on the body, but most frequently on the upper back of both sexes and on the legs of women Nodular melenoma .
NM occurs most often in the fifth or sixth decade.
It is found anywhere on the body. LMM usually presents in the sixth or seventh decade. The radial growth phase may last for years and never develop a vertical growth phase. The risk of progression of LM to LMM varies with age, but is lower than commonly believed. These risk estimates apply to patients in whom LM is discovered incidentally.