Absolute definitive diagnosis requires a biopsy. However, there are other reasons to perform the biopsy. The depth of penetration as measured on the biopsy will define the treatment and provide information about the prognosis.
However, a simple clinical diagnosis is often made using the acronym: ABCD
A = Asymmetry: if you divide the lesion in half is one side markedly different from the other?
B = Border; are the borders markedy irregular and ill defined with "bleeding" into the surrounding normal skin?
C = Color: does the lesion seem to be made up of differently colored portions (black, blue, brown, grey, red,etc)?
D = Diameter: is the lesion more than 6mm (1/4") in diameter?
A dermatologist may use more complex criteria based on a process called dermoscopy, which uses light and magnification to evaluate features that are not visible to the naked eye, such as blood vessels and pigment granules.
So to answer your question, biopsy is undeniably and important part of melanoma diagnosis and mangement
