Clark and Mihm

 
"Superficial spreading melanoma is characterized by a population of melanocytes appearing uniformly malignant; the striking melanocytic pleomorphism so characteristic of lentigo-maligna melanoma is not usually seen. Biopsy of the slightly raised hyperpigmented portion of superficial spreading melanoma reveals a 'pagetoid' distribution of large melanocytes throughout the epidermis. The large cells may occur singly or in nests and are uniformly atypical. Biopsy of markedly nodular areas of superficial spreading melanoma reveals, upon microscopic examination, dense accumulations of malignant cells in the dermis. In areas of invasion, large melanocytes are also observed. These large cells have an abundance of cytoplasm containing regularly dispersed fine particles of melanin; the 'dusty' appearance of the cells, when viewed with the microscope, is the result of these numerous granules. Occasionally, superficial spreading melanoma may show spindle cells and, rarely, a small cell that looks not unlike the cell of a mole. We, however, agree with McGovern (1968) that these cells are not nevus cells or cells of moles, but are small malignant melanocytes." (Fig. 5) Clark WH, Mihm MC. Moles and malignant melanoma. In: Dermatology in general medicine. New York: McGraw-Hill, Inc., 1971:506.

View Figure  		Fig. 5   Our diagnosis and comment: Melanoma in situ. The term "lentigo maligna" is an evasion from a diagnosis of melanoma in situ on skin damaged badly by sunlight, usually of a face. The histopathologic findings of melanoma in situ are the same on all anatomic sites. It is curious that although this legend was written by proponents of Clark's "histogenetic" classification of melanoma, those advocates failed to conclude that the pagetoid melanocytes in pagetoid pattern, shown here, were stereotypical for what they, themselves, call superficial spreading melanoma.
 

Brief Critique

 
The combination of atypical pagetoid cells in pagetoid pattern is highly suggestive of melanoma, but pagetoid cells, themselves, are not present with repeatability in melanomas on any anatomic site, including the trunk and proximal extremities (so-called superficial spreading type of melanoma). Moreover, pagetoid melanocytes with small monomorphous nuclei may be observed in certain congenital melanocytic nevi, especially ones biopsied early in life. In short, on the basis of the criteria offered in these lines of Clark and Mihm, a histopathologist would not be able to diagnose melanoma with specificity most of the time.