Diagrammatic Depiction of MDM
(variants of MDM in which “degrees of atypia” are a basic criterion)
In this diagram, levels of invasion (Clark’s criteria as modified in concept of MDM) are vertically stratified. Along the horizonal axis, degrees of atypia are represented along the horizonal lines from mild on the left to marked on the right (i.e., the common final pathway). Increasing bulk, as well as degree of invasiveness relate to level of invasion.Some melanomas may have their origin in a dysplasia in which degree of atypia is less than that of the common final pathway (i.e., MDM). Vertical growth is not simply a measure of depth of invasion. It is a pattern in which the close spacing of nests of cells to form a tumor is the basic requisite. The diagonal lines off the vertical axis define three boundaries along the bottom horizontal plane (level I & II). The domain to the left of the left-most diagonal line is that of the mild dysplasias. Between the left diagonal line and the middle line, the domain of the moderate dysplasias is represented. The domain between the middle line and the right-most diagonal line is that of the moderately severe dysplasias. Beyond the right line, the marked dysplasias are represented. The common final pathway (CFP) is represented in the domain of the marked dysplasias. In practice, the domain of the moderately severe dysplasias are oftenincluded in the domain of the common final pathway. The domains to the right of the left diagonal line, and above the bottom horizontal line are those of vertical growth components. Vertical growth, in association with lesser degrees of atypia than those of the common final pathway, defines this category of minimal deviation melanomas. There is no utility in characterizing patterns of lesions to the left of the left-most line as vertical growth and, then, accepting vertical growth as a marker for a melanoma. In this diagram, the reader might try to mentally represent a precise vertical dimension, such as the boundary for a borderland at 1 mm. The boundary cannot be represented in a manner that distinguishes between dysplasias (level I & II lesions) and melanomas (levels III and greater lesions). Levels of invasion are a measure of qualities that are independent of bulk. They have significance independently of the prognostic significance of bulk.