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MDM of Spitz-like type (continued)
In the concept of MDM, the primacy of both vertical growth patterns (herein, a vertical growth component, preferably of typical type, is the prime requisite for the definition of melanoma) and cytologic atypia have been given recognition in the definition of MDM of Spitz-like type (juvenile melanoma type). In such lesions, an identification of a remnant of the pattern of a typical “nevus” of Spitz-like type is a significant aid in the identification of transformed MDM of Spitz-like type. A remnant of a typical “nevus” of Spitz-like type provides a control with which the patterns in a compact nodule (i.e., vertical growth component) can be compared. Such a comparison of the patterns should provide evidence of cytologic disparity in the two sites. In the nodule, the cells will be more atypical with larger, irregular and hyperchromatic nuclei, more variable nucleoli, and a higher mitotic rate (often with atypical mitoses). In addition, the fascicles of cells forming the nodules may be coarse and usually are closely spaced. Often, the cytoplasms of the cells in the “vertical growth component” are intensely chromatic and lavender. The nodule may be associated with prominent lymphoid infiltrates, even manifesting the features of tumor infiltrating lymphocytes. Utilizing sets of virtual images which have relevance for the interpretation of MDM of Spitz-like type, variable patterns and cytologic details, which otherwise might have to be dismissed as inconsequential, can be molded into those of a MDM, or a borderline melanocytic neoplasm of indeterminate malignant potential (Spitz-like variant).
In current practice, nodules with cytologic disparity, cytologic atypia, atypical mitoses, and abnormal patterns of aggregation of nests of cells are either accommodated by most pathologists in a liberal definition of Spitz “nevus,” or lesions displaying these features are mistakenly assigned to the default category of common melanoma. Currently, an expansile nodule which is composed of atypical cells in broad, compactly arranged fascicles and is associated with a neighboring component of more typical cells in more typical patterns (transformed or classic MDM of Spitz-like type) is likely to be assigned to a category of Spitz “nevus” without appended qualifications. A similar nodule of atypical cells (de novo MDM of Spitz-like type) lacking a marker for a pre-existing Spitz “nevus” is likely to be dismissed as a common melanoma. In view of the infrequent encounters with, and the poor documentation of either of the two variations, it would be premature to assume that the two variants are biologic equivalents.
Following the definition of Spitz “nevus” as a benign process, there have been occasional reports of metastases (mostly limited to one or a few regional lymph nodes) from lesions with the “characteristics” of Spitz “nevus.” Rather than assigning primacy to any deviant pattern in these examples, and promoting the deviant patterns as the basis for the definition of significant variations in the Spitz category, most of the emphasis has been on the variant patterns as an additional parameter in the sets of virtual images defining Spitz “nevus,” and in an extension of the biologic spectrum of typical Spitz “nevus.” It is as if the nodal metastases are a biologic accident, and should be accepted and ignored, rather than cited as the basis for the recognition of significant neoplastic progression, as manifested in histologic variations in the primary lesion. Metastasizing Spitz “nevi” probably are morphologically distinctive when compared with the patterns of the most common type of Spitz “nevus.” Some of the metastasizing lesions satisfy the criteria for the recognition of MDM of Spitz-like type. With few, if any, exceptions, metastasizing Spitz “nevus” is MDM of the Spitz-like type, or a more aggressive melanoma of non-Spitz type masquerading in Spitz-like patterns (i.e., a high grade fascicular, spindle cell melanoma with variant vertical growth patterns). Some examples are associated with a population of common nevus cells, and on the basis of combined patterns might also qualify as MDM of the combined “nevus” type. Some of the latter lesions have behaved in the fashion of true melanomas with widespread metastases.
An arbitrary assignment of an atypical lesion to the category of Spitz “nevus” may require the manipulation of virtual images, if such a lesion is later associated with evidence of metastases. If, following the assigment of such a primary lesion to the category of Spitz “nevus,” regional nodal metastases are discovered, the primary lesion might, in retrospect, be re-assigned to the category of “metatasizing Spitz nevus;” the deviant histologic features might then be dismissed as being within the spectrum of Spitz “nevus,” and the metastasis as “benign.” The other option would be to ignore the Spitz nevus-like qualities, and to re-assign the lesion to the category of common melanoma, or to characterize the lesion as “Spitz-like” melanoma. Similar scenarios can be developed for problematic lesions in the category of combined “nevus.” All these scenarios find promotion by various experts in the engagements of malpractice proceedings. In these shenanigans, the force of personalities of “experts” tend to overshadow the ambiguities; the ambiguities then can be exploited, and raised to the level of contentions.
Once an accommodation has been made for MDM of the Spitz type, in which a remnant of a more characteristic Spitz “nevus” is preserved, it requires little effort to extend the definition to include examples in which a remnant of a typical Spitz “nevus” is not represented (i.e., de novo MDM of Spitz-like type). In these extensions, care must be exercised. Some lentiginous melanomas, including some examples of LMM and ALM, in which the vertical growth component is composed of plump spindle cells, have qualities that may be confused with those of MDM of the Spitz-like type. Such lesions cannot be easily and comfortably assigned to a category of MDM of Spitz-like type, or to a category of a common melanoma; they can be assigned to a category of melanoma, not otherwise classified, but the appropriateness of an evaluation by Breslow’s criteria might be questioned. If such a lesion has metastasized, it is likely to be characterized as either “Spitz-like” melanoma or “metastasizing Spitz nevus.”
In regard to prognostications by histologic evaluations, MDM of the Spitz-like type is exceptional. By nature, most “Spitz” variants are level (pattern) IV lesions and, if evaluated by Breslow’s criteria, many will have sufficient bulk to be characterized as ominous. Caution is recommended in the manipulation of the usual prognostic parameters in the evaluation of MDM of the Spitz-like type. Time has confirmed this wisdom. In fact, some of the “metastasizing Spitz nevi” (MDM of Spitz-like type) have been small, rather thin lesions whose potential for metastasis would not have been anticipated by evaluations with the usual parameters. Others have been large, but have behaved in a benign fashion. As an alternative, these lesions might be characterized as melanocytic neoplasia of indeterminate malignant potential (Spitz-like type). In this approach, some of the lesions would eventually prove to be truly melanomatous in character with both nodal and distant metastases. These metastasizing variants would have been accommodated therapeutically by recommendations for conservative re-excision of the primary site and for follow-up. To continue to guess as to the biologic potential of each disturbing lesion would only foster controversy; many of these lesions would be assigned to the category of melanoma. There would be no uniformity and no basis for interobserver agreement. There would be considerable freedom for the manipulation of clinical data, diagnoses, and linguistics by trial lawyers.
Currently, in the category of melanoma, there are few provisions for modifiers of histologic type that will also relate to differences in biologic behavior. If a lesion, provisionally touted to be a melanoma, deviates from established relationships between current prognostic parameters and biologic behavior, it is likely that the lesion will be assigned to a category other than that of common melanoma; MDM of the Spitz-like type is an example.
The following designations have application in the manipulation of images in the Spitz-like category:
1. atypical Spitz (spindle cell) melanocytoma (“nevus”) (melanocytic dysplasia of Spitz-like type)
2. MDM of Spitz-like type (including “metastasizing Spitz nevus”)
a. variant vertical growth-like patterns (patterns basically those of atypical Spitz-like melanocytoma but with greater vertical dimensions)
b. typical vertical growth-like patterns
3. melanoma with Spitz-like qualities (generally a problem in the lentiginous category)
a. large cell variant (usually pleomorphic)
b. small cell variant (usually bland cytologically but with a definite propensity for metastasis)
(Note: Spitz “nevus” and all its related variants may be composed in part, or entirely, of pigmented spindle cells)
All the above variations can be accommodated by assigning all variant lesions with “vertical growth components” to a category of intermediate neoplasia of Spitz-like type (Note: nuclear grade II-III, or even IV [anaplasia], and cytologically epithelioid in both spindle and round cell configurations). In this accommodation, some of the peculiar lesions with “spitzoid” features that are not readily classified in other categories will prove to be aggressive, metastasizing melanomas, with both regional and distant metastases.
Pigmented spindle cell “nevi:”
The category of pigmented spindle cell “nevi” (melanocytomas) is heterogeneous. Some examples evolve at the dermal-epidermal interface, and usually are thin lesions when first diagnosed and excised. On the other hand, the common variant of combined “nevus” and deep penetrating “nevus” are lesions with more significant vertical dimensions; they are closely related and are sometines associated with lentiginous and junctional patterns. Blue nevus, nevus of Ota and Ito, and cellular blue nevus are also variants of pigmented spindle cell nevus (Note: some examples of cellular blue nevus are amelanotic). In giant congenital nevus, as a regional variation, spindle cell patterns are occasionally a feature.
Pigmented spindle cell “nevus” of Reed (PSCN) is more common in adults than children. A woman’s thigh is a peculiarly favored site. PSCN is not a marker for the dysplastic nevus syndrome. A common clinical impression is “melanoma.” PSCN evolves in minor lentiginous, and major junctional patterns at the dermal-epidermal interface. In the epidermal component, fascicles of thin, pigmented spindle cells are closely spaced; they commonly are confluent across several rete ridges. Fascicles may also infiltrate the epidermis above the basal layer. In them, the cells tend to be arranged with their long axes parallel to the skin surface. The nuclei have slightly open chromatin patterns and a small, central nucleolus (nuclear grade I). There is remarkably symmetry and if, focally, the fascicles extend into the papillary dermis, they tend to cluster to form a solid plaque or nodule; the solid portion pushes into the dermis. The nodule, if represented, tends to be centrally placed and, on both sides of it, the lentiginous and junctional components are equally distributed. The nodule may be confined to the papillary dermis but, for some examples, thin fascicles and individual cells may infiltrate the reticular dermis among the collagen bundles (a Spitz nevus-like quality). Maturation is a prominent feature, and cells and their nuclei are smaller in the deeper portions of the lesion. Lymphoid infiltrates at the interface between the nodule and the dermis generally are not a prominent feature.
If pigmented spindle cell “nevus’ of Reed has an atypical counterpart and, if the atypical counterpart is accepted as a marker for neoplastic progressions, we should anticipate that some examples will progress to become deceptively bland pigmented spindle cell melanomas. Some MDM of pigmented spindle cell type (lesions that have lost distinguishing features of pigmented spindle cell “nevus,” and have metastasized) may be transformed pigmented spindle cell “nevus.”
Pigmented spindle cell “nevus” of Reed is not a marker for the dysplastic “nevus” syndrome. The spotty, irregular patterns of premalignant dysplasias in the setting of the dysplastic “nevus” syndrome contrast sharply with the uniform patterns and symmetry of PSCN.
It has been argued that PSCN is nothting more than a pigmented variant of spindle cell “nevus” of Spitz type. The two differ cytologically, in aggregate patterns, and in clinical settings. The differential diagnosis of PSCN is unlikely to include angioma (a common clinical characteristic of Spitz “nevus,” but is likely to include premalignant dysplasias and melanoma. To include the PSCN in the category of Spitz “nevus” would require an expansion of the definition of pigmented, but otherwise classic, Spitz “nevus.” The general Spitz-like category would be enlarged; modifications in the accepted criteria for recognition of Spitz-like variants would be required. In short order, the addition would be recognized as an intruder in the Spitz category and would then be reassigned to a separate category. From a review of pictorial documentation in early reports, it is likely that some examples of PSCN have been included in the Spitz category. Contrarily, some examples of pigmented Spitz “nevus” probably have been included in the category of PSCN. Invariably, in the definition of new disorders, the initial efforts are too broad, and the new category initially is heterogeneous.
In atypical PSCN, the basic patterns are preserved but the cells at the dermal-epidermal interface have plump, elongated nuclei with delicate chromatin, irregular nuclear outlines, and prominent central nucleoli. Markers for host immune response, including lymphoid infiltrates and papillary dermal fibrosis, are variable features, and are more common in examples exhibiting nuclear grade II. Mitoses are more common in the atypical variants. For atypical variants in which the dermal component forms an expansile nodule, a decision to classify respective lesions as either atypical spindle cell “nevus” or MDM of the pigmented spindle cell type becomes an arbitrary choice which would be difficult to defend.
For atypical spindle cell “nevus” of Reed in which cytologic atypia and overall bulk of tumor raises the question of a diagnosis of MDM, an alternate designation might be borderline melanocytic neoplasia of indeterminate malignant potential (PSCN variant, nuclear grade II).
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