BWEEMS

Minimal Deviation Melanoma

A SITE DEDICATED TO EXPOSITIONS OF THE PATHOLOGY OF UNUSUAL MELANOCYTIC LESIONS

RICHARD J. REED, M.D.

ROOM 302, 234 LOYOLA AVE., NEW ORLEANS, LA. 70112

E-MAIL: rjrpjrlr@aol.com

This site is dedicated to the presentation of unusual  melanocytic lesions. The focus will be biased and will emphasize concepts of melanocytic neoplasia as developed in the concept of MINIMAL DEVIATION  MELANOMA. The structure of this site will be rather simple at 3 tiers. The first tier will always be a single page (HOME); it serves as an introduction. Usually, there will be no more than three pages along the horizontal axis of each of the other two tiers. You currently are at the HOME PAGE or the 1st TIER. The border to the left and above is the MASTER BORDER. In it, navigation bars will be displayed. The HOME PAGE will be identified as to topic on on the first bar of the collection of purple navigation bars - the subject under discussion will be identified. For this presentation, the bar identifying the HOME PAGE is labeled, MDM HALO (i.e., minimal deviation melanoma, halo nevus-like type). The second tier will include an index and a textual page. The third tier will be a pictorial level. Navigation bars leading to the 2nd and 3rd levels will, with a click, take the reader to TIER 2 and TIER 3 respectively. Underlined words in the text should be examined with the cursor to identify words which, when clicked, can serve as a link to other portions of the structure. The browser’s back button will be an aid in the navigation along the tiers.

The concept of MINIMAL DEVIATION MELANOMA  provides a set of tools for the manipulation of virtual images (see WhithersI, II, & III) . In part in the histologic evaluation of a melanoma, bulk relates to prognosis; in addition, a single dimension measured along the vertical axis of the vertical growth component serves as a measure of "bulk;" a measurement of a single dimension in the structuring of progostications has utility; within certain ranges of sizes (i.e., thin vertical dimensions), the risk of a metastasis or local recurrence in vertical growth patterns is so low that it is inappropriate to characterize some of these lesions as "melanomas" without additionally providing some type of disclaimer. One variant of minimal deviation melanoma is a thin, common melanoma (i.e., a lesion that is less than 1 mm in vertical dimensions); it is the most common variant; such a lesion also qualifies as a melanocytic  neoplasm of uncertain or indeterminate malignant potential (with distinctions based on two ranges in size). Lesions less than 1 mm in vertical dimensions are borderline processes of indeterminate malignant potential. Lesions in the range of 1 to 1.5 mm in vertical dimensions are intermediat variants of indeterminate malignant potential. The  other examples of MINIMAL DEVIATION MELANOMA might be characterized as the NEVOID VARIANTS. Some of these variants can also be qualified on the basis of limited vertical dimensions.

Minimal deviation melanoma as a concept dates from the mid -70's. A good many of the evaluations of the concept have mostly been concerned with attempts to discredit it, or to restrict the definition to one particular variant. Little to be said in defense of the concept. To defend it would be much like defending the notion that some of us see ghosts. If you see ghosts you are likely to believe in them, and if you believe in them, you are likely to see them.

A part of the concept of MDM gave recognition to thickness, or even diameter of vertical growth components as a measure of the age of a problematic melanocytic neoplasm. In this approach, a small, thin lesion would likely be a "young" neoplasm. In turn, with the presumption that melanocytic neoplasia advances not only in size but also clonally (late lesions genetically would be further removed from benign neoplasia than would early or young lesions), early lesions in vertical growth are likely to be less atypical cytologically than late lesions. In addition in many examples, there are, with advancing age of neoplasia, also changes in patterns of vertical growth. In young, thin lesions that are evolving in the setting of premalignant dysplasias, the vertical growth patterns are likely to be those of arrested variant vertical growth (see WHITHERS1 , WHITHERS2,andWHITHERS3).

A later, but not invariable stage in the evolution of young lesions, might include variant vertical growth with an activated stroma. Variant vertical growth basically is a particular pattern that is confined to the stroma of a widened papillary dermis. With advancing neoplastic age  (sequential neoplastic progressions), most of the evolving lesions in the setting of premalignant dysplasia will eventually show the emergence of a typical vertical growth component. Typical vertical growth differs in patterns from variant vertical growth but is also confined to a widened papillary dermis; generally its interface with the reticular dermis is defined by a band of condensed, inflamed fibrous tissue. Vertical growth at level III, as defined above, can progress in bulk to produce a large, bad prognosis lesion. In some  examples at any stage in the evolution of the vertical growth component (in thin or thick level III lesions), the lesion violates the reticular dermis with infiltrating patterns; the tumor infiltrates among collagen bundles of the reticular dermis (level IV pattern); this change in the relationship between tumor cells and "stroma" qualifies as migrant vertical growth; it often is accompanied by a change in host immune response; the tumor tends to infiltrate the reticular dermis without evoking a prominent immune response.  In all the variations, the concept of minimal deviation melanoma is available as a tool for the evaluation of premalignant dysplasia related-melanomas. It allows the pathologist to gauge age of neoplasia by correlating size, patterns of vertical growth, and cytologic features. Size is so important that it might be proper to speak of premalignant and young, malignant, melanocytic neoplasia measuring less than 1 mm in vertical dimensions as borderline melanocytic neoplasia of indeterminate malignant potential. It is also appropriate to then define another boundary at 1.5 mm and to label lesions in the range of 1-1.5 mm as intermediate melanocytic neoplasia of indeterminate malignant potential. So much for thin, evolving lesions in the category of the premalignant dysplasia-melanoma sequence.

Of equal significance in the structuring of the concept of MDM (if the concept of MDM actually has significance) was the relevance of typical vertical growth patterns for the definition of variant melanomas (i.e., "nevoid" melanomas that, by a display of variant nevus qualities and by their bland or unusual cytologic features, might easily be mistaken for a variant nevus). In this approach, the  category of variant minimal deviation melanomas included: 1.) halo nevus-like variant, 2.) Spitz nevus-like variant, 3.) pigmented spindle cell variant, 4.) combined nevus-like variant, 5.) dermal variant (including common form and congenital nevus type), and 6.) blue nevus-like variant. The category of nevoid minimal deviation  melanoma can accommodate all these variants. It also includes examples, which in patterns and cytologic details, might be mistaken for a peculiar, atypical common nevus. Even in the categories of the  common melanomas, there are examples of lentigo maligna melanoma  (LMM) and acral lentiginous melanoma (ALM) that on the basis of patterns and cytologic details qualify as minimal deviation variants. Desmoplastic (see second white navigation box in vertical masterborder to the left) and neurotropic melanomas, early on, commonly are deceptive histologically and would qualify as minimal deviation variants.

 This site will be dedicated to a presentation of the  histologic features of variant melanomas and other melanocytic lesions. A brief discussion of significant histologic features will be a part of each presentation.

Note: In the second white navigation bar, a click on “REACTION PATTERNS OF INFLAMMATION” will take the reader to a separate web site.

In navigating this site, there will be navigation bars beyond the level of the text. Continue to the end of each page (the limits of downward movement with the browser) to view all the navigation aids.