What is the importance of Clark's level in melanoma diagnosis?

The Clark Level of Invasion scale helps estimate life expectancy in patients with melanoma, according to MedicineNet. The scale stages the melanoma lesion based on how far it has penetrated through the skin.

According to Clark's scale, a Level I melanoma is confined to the top layer of skin, the epidermis, explains MedicineNet. Level II through IV melanomas have penetrated into the dermis and are graded by how deeply they infiltrate into this layer. Level V melanomas have infiltrated into the third layer of skin, the fat beneath the dermis. Although Clark's level may be used to determine melanoma prognosis, Breslow's thickness, a method that relies on the size of the tumor, is more commonly used.