Pinkus and Mehregan

 
"Criteria for malignancy of a melanotic tumor are several, and some are more significant than others. Presence of mitoses is of primary importance, although some mitotic figures may be found in benign juvenile melanomas and an occasional one even in benign nevi. Absence of mitosis does not rule out malignancy. The next important feature is inflammatory reaction composed of lymphocytes and possibly plasma cells. It is practically always present, but may also be found in benign juvenile melanoma, nevus incipiens, and Sutton's halo nevus. It must not be confused with the acute or granulomatous infiltrate that may be caused in a benign intradermal nevus by infection of a hair root or breakdown of a follicular cyst. Cells of malignant melanoma usually are much larger than even the large A type cells of benign nevi, a feature also true for benign juvenile melanoma. One should not be confused by large multinucleated nevus giant cells occurring in benign lesions. Distribution and amount of pigment usually is more variable in malignant melanoma, some nests containing much, others little or none. Particularly characteristic is dustlike pigmentation of large celled junctional nests. One should of course not be deceived by the presence of pigmented macrophages which occur in benign as well as in malignant lesions . . . Another factor helpful in some cases is the constitution of the dermal stroma. It was mentioned earlier that nests of benign nevus cells are often surrounded by collagen bundles, and even in their absence by fine elastic fibers and reticulum fibers making an orderly and distinct pattern. This is not so in malignant melanoma which outgrows and destroys stroma. Elastic fiber and reticulum stains assist in differential diagnosis between benign and malignant intradermal tumors." Pinkus H, Mehregan AH. A guide to dermatohistopathology. New York: Meredith Corporation, 1969:381–83.
 

Brief Critique

 
As Pinkus and Mehregan acknowledge, the presence or absence of mitotic figures in abnormal melanocytes, atypical nuclei of melanocytes, and infiltrates of inflammatory cells are not helpful in differentiating a melanoma from a Spitz's nevus. The same is true, equally, for multinucleate melanocytes, amount of melanin, dustlike melanin in abnormal melanocytes, and stromal changes. For example, melanin may be distributed in asymmetrical or uneven fashion in certain combined congenital melanocytic nevi, dustlike melanin may be seen in some congenital nevi biopsied shortly after birth, and stromal changes, such as desmoplasia that destroys elastic fibers, may be observed in some Spitz's nevi, as well as in some melanomas.