|
Variants of Melanoma (lesions not of the type: other nevi, other variants of melanoma, and other borderlands)
Note: For lesions in this SECTION, size alone is not always the chief criterion for the delineation of a borderline category)
In practice, Breslow’s criteria and the related guidelines to treatment have removed the onus from characterizations of a variety of thin melanocytic lesions as “melanomas.” In this limited range in which lesions are thin (i.e., 1 mm or less in vertical dimensions), a degree of relativity in the diagnosis of melanoma is unavoidable. Many surgical pathologists, even when confronted with variant histologic patterns, still react to the diagnosis of melanoma as if there is no provision for relativity, or for degrees of malignancy. For this group of observers, utility is not embodied in the concept that size of a vertical growth component has relevance in estimating the age of the respective neoplasm, nor is it intrinsic in the proposition that age of a neoplasm, and grade of neoplasia commonly are related. Variant histologic features in young lesions would not be appreciated by these observers as a possible marker for an early stage of neoplastic progression.
Many surgical pathologists react to the diagnosis of melanoma as if the expanse of segments of neoplastic continua, which they have individually selected and currently are utilizing, are inviolate. They consider modifications of their selected segments, or alterations of existing categories as a desecration of what has for them become sacred principles of neoplasia. Segments such as “melanoma-in-situ,” “melanoma” at level II, and high grade dysplasias, though stoutly defended by proponents, have not been chiseled in stone, and then brought down from the Mount; these segments are so insignificant biologically that they might be offered in support of the concept of relativity in the diagnosis of melanoma.
If we can accept relativity in the category of the common melanomas, then a slight modification of our virtual images might provide accommodation for variants of “melanoma,” including a Spitz nevus-like variant. In these accommodations, it would not be necessary to then assume that such a lesion has the same biologic potential as a common melanoma with comparable physical dimensions. Prognostic evaluations and therapeutic recommendations could be altered, and modified to accommodate variants.
Variants of nevi are well-defined. They provide the basis for a definition of variant dysplasias (the atypical “nevi”) and variant melanomas.
Atypical nevi and their relationship to certain variant (minimal deviation) melanomas:
In general, the combination of patterns of a typical nevus, and of premalignant melanocytic dysplasia (as commonly manifested in lesions of the dysplastic nevus syndrome) identifies the respective lesions as atypical “nevus” (conceptually, such a lesion is a dysplasia in continuity with a remnant of a nevus). An extension of this definition has application in the recognition of atypical halo “nevus,” atypical “Spitz nevus,” atypical combined “nevus,” and atypical pigmented spindle cell “nevus.” Atypical “nevus” of dermal type, and atypical cellular blue “nevus” are exceptions; representations of the epidermal patterns of premalignant melanocytic dysplasia are not a requisite; the neoplastic component, the dysplasia, is of dermal type.
Atypical halo “nevi”of junctional type show the basic patterns of typical halo nevi but, in addition, are characterized by features of premalignant melanocytic dysplasia in lentiginous and junctional patterns; the epidermal component extends in the epidermis away from any dermal components. In atypical halo “nevi” of junctional type, the qualities of both halo nevus and atypical nevus of the dysplastic nevus syndrome are combined. Just as there are atypical halo “nevi,” in which the patterns of premalignant melanocytic dysplasia are combined with those of typical halo nevus, there are examples of spindle cell “nevus” of the Spitz type in which patterns of premalignant melanocytic dysplasia are represented. Some examples of atypical spindle cell “nevus” of Spitz-like type are mostly lentiginous and junctional with minimal or no dermal components.
The concept of “junctional nevus” of Spitz-like type carries with it the implication that if left undisturbed, such a lesion would evolve into classic Spitz nevus. In addition, there is the implication that if all Spitz “nevi” could be examined at the proper moment, the pattern would be that of “junctional” Spitz “nevus.”
“Junctional nevus” of Spitz type is usually an atypical “nevus.” Such lesions usually show nuclear atypia, upward migration of individual tumor cells into the epidermis, and markers for host immune response (lymphoid infiltrates and dermal fibrosis, often in lamellar patterns). In these variations, there may or may not be a lesion centrally with the features of either a classic Spitz “nevus,” or MDM of the Spitz-like type. From the perspective promoted herein, the “junctional” Spitz “nevus” is usually atypical. In prognostications for such lesions, it might be more appropriate to anticipate that such a lesion, if undisturbed, would evolve into a MDM of Spitz-like type.
For those lesions with features of both a variant “nevus” and a melanoma, some examples may also share features of premalignant melanocytic dysplasias, but the most important shared attribute is the presence of a vertical growth component. Some MDM of halo nevus-like type are not associated with a radial component (i.e., lentiginous and junctional spread in the epidermis away from both the vertical growth component and the remnant of the dermal component of a pre-existing halo nevus). On the other hand, many are. Some of the latter examples most likely have had their origin in atypical halo “nevi.”
In MDM of both halo nevus-like type and Spitz-like type, patterns, that have the attributes of a dermal remnant of a benign nevus, often are preserved adjacent to the nodule of atypical cells. Many examples of MDM of Spitz-like type are associated with markers for a remnant of an atypical “nevus” of Spitz-like type, the implication being that these MDM have had their origin in atypical Spitz-like “nevi.” These attributes include lentiginous and junctional patterns of a dysplasia (i.e., radial growth component), a nodule of cytologically atypical cells (i.e., typical vertical growth component), and markers for host immune response. If comparisons are made, the cytologic features of cells in the remnant, and the cells in the nodules will prove to be disparate, with atypia being a feature of the cells in the nodules. Some Spitz nevus-like lesions have a vertical growth component, but not all these melanoma-like lesions are associated with radial spread in patterns that might be characterized as a remnant of an atypical “nevus” (spindle cell melanocytoma) of Spitz nevus-like type.
In these and other examples of variant melanomas, the basic patterns of a benign variant nevus may be preserved but, focally, or relatively uniformly, the component cells are atypical, and show mitotic activity. In some variants, such as MDM of the dermal type, and halo nevus-like type (dermal variant), the cytologic atypia is moderate to moderately severe, and the cells are relatively uniform in regard to nuclear characteristics. The nuclei tend to be intermediate in size with an increased prominence of nucleoli.
In at least one example of MDM (i.e., Spitz-like variant), nuclear atypia and cytologic pleomorphism are often prominent features. The features may be sufficiently developed to qualify as large cell anaplasia. In contrast to the bland nuclear qualities commonly manifested in MDM arising in the setting of the dysplastic nevus syndrome, the nuclear grade of MDM of the Spitz-like type usually is high. Often the neoplastic cells of such lesions show distinctly lavender, or basophilic cytoplasm but, in other examples, the cytoplasm of the tumor cells, in common with ordinary “nevi” of Spitz type, is acidophilic.
All the variant melanoma-like lesions, with some features which overlap with those of variant “nevi,” but with other deviant features that are melanoma-like, have been included as special variants of “melanoma” in the category of MDM. The latter concept has the utility of providing separate categories for deviant lesions and, in addition, for providing guidelines for the management of lesions with poorly defined biologic potentials (melanoma-like lesions of uncertain, or indeterminate biologic potential). Poorly defined biologic potentials would justify the inclusion of these variant lesions in separate categories of borderline melanocytic neoplasia of indeterminate malignant potential.
The variants of “nevi” and malignant or borderline counterparts include:
1. typical (common) nevus:
a. atypical (dysplastic ) “nevus”
b. thin, common malignant melanoma (most often expressed as a common final pathway in radial growth (i.e., SSM)
c. malignant melanoma measuring greater than 1 mm but less than 1.5 mm in height
2. genital “nevus”
a. atypical genital “nevus”
b. melanoma of genital nevus-like type
3. halo “nevus” (halo “nevus” probably has taken a step beyond the nevic category; it probably is a neoplasm, whether of junctional or dermal type)
a. atypical halo “nevus”
b. MDM of halo nevus-like type (lentiginous and junctional dysplasia type)
c. MDM of halo nevus-like type (dermal dysplasia type)
4. Spitz “nevus” (juvenile melanoma, step I type)
a. atypical “nevus” of Spitz-like type (atypical spindle cell melanocytoma of Spitz-like type)
b. MDM of Spitz-like type; including examples arising in Spitz “nevus,” examples in atypical Spitz “nevus,” examples that might otherwise be classified as combined nevus of Spitz type, and de novo examples
c. melanoma with Spitz nevus-like features (spitzoid?)
5. combined “nevus” of common type (including deep penetrating “nevus”)
a. atypical combined “nevus”
b. MDM of combined type
6. pigmented spindle cell “nevus”
a. atypical pigmented spindle cell “nevus”
b. MDM of pigmented spindle cell type (non-Spitz type)
7. blue nevus (including nevus of Ota and Ito)
a. pigmented spindle cell melanoma
b. combined nevus of blue nevus type
Continued on next page - CLICK
|
