Answer:
Clark and associates defined the following five levels of invasion:
Level I—the atypical melanocytes are confined to the epidermis (in situ melanoma).
Level II—the atypical melanocytes have extended into the papillary dermis but have not reached the reticular dermis.
Level III—the atypical melanocytes have penetrated to the interface between the papillary dermis and the reticular dermis but do not extend into the reticular dermis.
Level IV—the atypical melanocytes have extended into the reticular dermis.
Level V—the atypical melanocytes have reached into the subcutaneous fat.
Breslow related prognosis to the maximum thickness of the lesion as measured by an ocular micrometer from the top of the granular zone of the epidermis to the base of the neoplasm. This method is preferred because it is the single most accurate indicator of prognosis, and it is consistently reproducible among different pathologists.