• Lack of the classical findings of the radial growth phase of a melanoma though atypical intraepidermal hyperplasia or dysplasia may be present.
• The presence of an expansile nodule or nodules within the dermis that are composed of melanocytes that are atypical but which lack the severity of atypia that would be easily diagnosed as melanoma.

There are subsets of this class of melanocytic lesions^{ref 4}  including those of halo nevus type^{ref 5}. The concepts associated with minimal deviation melanomas are being continually refined^{ref 6}.

It should be mentioned that the presence of expansile nodule/s may not be required for rare lesions having minimal deviant cell populations (usually spindle cells) in dispersed or fascicular patterns. The assignment of such lesions to the minimal deviation melanoma category belongs in the realm inhabited by consultant pathologists having more experience than I.
 
 

The observation of lymph node metastases in the absence of visceral metastases deserves examination. This phenomenon brings to mind papillary adenocarcinomas of the thyroid gland. Cervical lymph node metastases are common in this setting, but a lethal outcome is extremely rare in the face of such metastases unless there are markers of increased risk in the primary lesion (such as invasion of the thyroid capsule). The capability for lymph node metastases appears to be qualitatively different than the ability to establish proliferating colonies in visceral organs. That the two capabilities often coexist in ordinary, fully developed melanomas does not necessarily imply that this occurs in minimal deviation melanomas. The character of the primary lesion may, as in thyroid papillary adenocarcinoma, be significant. There are obvious prognostic and therapeutic implications inherent in this concept.

If for no other reasons than those stated above, it would be desirable to study minimal deviation melanomas as a subset of melanomas. This would require the inclusion of this category in future melanoma study protocols. It is anticipated that more cases with subclinical lymph node metastases will become eligible for study given the growing popularity of sentinel lymph node examination.

1: Carson KF, Wen DR, Li PX, Lana AM, Bailly C, Morton DL, Cochran AJ.
                       Nodal nevi and cutaneous melanomas.
                       Am J Surg Pathol. 1996 Jul;20(7):834-40.

2: Reed RJ.
                       Minimal deviation malignant melanoma arising in a congenital nevus.
                       Am J Surg Pathol. 1978 Jun;2(2):215-20.

3: Muhlbauer JE, Margolis RJ, Mihm MC Jr, Reed RJ.
                       Minimal deviation melanoma: a histologic variant of cutaneous malignant  melanoma in its vertical growth phase.
                       J Invest Dermatol. 1983 Jun;80 Suppl:63s-65s.

4: Reed RJ, Martin P.
                       Variants of melanoma.
                       Semin Cutan Med Surg. 1997 Jun;16(2):137-58.

5: Reed RJ, Webb SV, Clark WH Jr.
                        Minimal deviation melanoma (halo nevus variant).
                       Am J Surg Pathol. 1990 Jan;14(1):53-68.

6: Reed RJ.
                       Dimensionalities: borderline and intermediate melanocytic neoplasia.
                       Hum Pathol. 1999 May;30(5):521-4.

7: Smith KJ, Barrett TL, Skelton HG 3d, Lupton GP, Graham JH.
                       Spindle cell and epithelioid cell nevi with atypia and metastasis (malignant Spitz nevus).
                       Am J Surg Pathol. 1989 Nov;13(11):931-9.

8: Donner LR, Manriquez M, Greene JF Jr.
                        Minimal deviation spindle cell melanoma: unusual histologic pattern in an 11-year-old black  girl
                        Pediatr Pathol. 1988;8(4):401-7.

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