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Spindle Cell Melanocytic Lesions
In spindle cell melanocytic lesions, certain features are fairly common. Epithelioid cells are acceptable in spindle cell lesions. Spindle cell lesions are likely to be expressed in fascicles. Often the fascicles are loosely spaced in both the papillary dermis, and among collagen bundles of the reticular dermis. For some examples, fascicles of spindle cells may extend through the papillary dermis without inducing a significant hyperplasia of the stroma. In the reticular dermis, benign and malignant spindle cell lesions tend to infiltrate among collagen bundles in patterns that might be characterized as migrant vertical growth-like (if the lesion is to be characterized as benign) or migrant vertical growth (if the choice is to classify the lesion as malignant). In the reticular dermis in malignant variants, the host immune response often is minimal.
Spitz nevus-like variants display the above characteristics. It may be difficult to distinguish between a Spitz nevus-like variant, and a more common spindle cell melanoma as manifested in the setting of lentigo maligna melanoma, or acral lentiginous melanoma, or even a nevoid spindle cell melanoma. Emphasis must be placed on cytologic features; the results of such an evaluation may not be definitive for some lesions. Some examples of lentigo maligna melanoma, in both vertical growth patterns and cytologic features, may closely resemble a Spitz variant.
In the category of minimal deviation melanoma of Spitz nevus-like type, the original definition of such a lesion required the presence of a typical vertical growth pattern (a rather solid, expansile nodule). A lesion with only variant and migrant vertical growth patterns would be more problematic in regard to offering justification for the assignment of such a lesion to the minimal deviation category. The minimal deviation category has been much abused by its critics. If, however, we examine some of the photomicrographs in published descriptions of “Spitz nevus” and related variants, nodular components are encountered; the authors of such contributions tend to ignore this deviation from classic Spitz pattern.
In a recent article in the Am J Surg Pathol (26:654-661, 2002), Fig. 4a presents the pattern of an atypical spindle cell melanocytoma of Spitz nevus-like type. In Fig. 4b, the expansile nodule in the dermis is, if nothing else, typical vertical growth-like. With adequate documentation of cytological features, it could well represent a MDM of “Spitz nevus-like” type. In Fig. 6 a&b, the patterns are those of a MDM of spindle cell type (possibly pigmented spindle cell type; the cytologic features as represented at low magnification are not clearly Spitz nevus-like). In these two figures, the patterns are those of migrant vertical growth (fascicles of cells infiltrating among collagen bundles of the reticular dermis), but the lesion is clearly an expansile nodule and atypical. In Fig. 8c, the patterns in the reticular dermis are clearly those of migrant vertical growth.
In another recent article (Am J Surg Pathol 26:47-55,2002), Sentinel lymph node biopsy is promoted for lesions in the “spitzoid melanocytic” category. To characterize the cellular, diffuse patterns of Figs. 1 as those of a desmoplastic Spitz lesion (if an observer finds himself unable to assign a problematic lesion to either a benign or malignant category, the qualifier, “Spitz,” tends to impose the virtual images of a benign process; an alternative to “Spitz nevus” is often required but “Spitz tumor,” a designation which offers little in the way of specificity, seems to be inappropriate. There is prominent cytologic atypia even at the inadequate magnifications selected for the photos (the current trend in the literature is to publish inadequate, small photomicrographs; is this a choice of the authors or an imposition by the editors?). I find MDM an appropriate designation for many problematic lesions. A characterization of the patterns as having Spitz nevus-like qualities would be somewhat misleading; perhaps, the lesion might be characterized as MDM, ambiguous phenotype. The patterns in Fig. 2 are Spitz lesion-like but the cytologic features are deviant. There are Kamino bodies in the junctional nests and, perhaps, the authors have resolved the dilemma posed by LeBoit. The lesion might be best characterized as Spitz nevus-like, and as melanocytic neoplasia of indeterminate malignant potential. It would appear to be less than 1 mm in vertical dimensions; it would additionally qualify as borderline (on the basis of physical dimensions). In Fig. 3, the adage, that a Spitz variant should share features with Spitz nevus, has been ignored. There is an irregularly expansile nodule which, in the reproductions, appears to be in a widened papillary dermis (i.e., typical vertical growth pattern). In the nodule, fascicles are closely aggregated with little or no intervening stroma. The cytologic features of cells in the nodule are not Spitz-like. When the cytologic features of cells forming the clustered nests near the arrow in Fig. 3b are compared to the cells in the nodular component, the features are discordant. The nodule is acceptable as a vertical growth component; the patterns can be accommodated in the category of MDM (either Spitz-like or spindle cell type). The lesion lacks a number of features commonly emphasized in the diagnosis of Spitz-like lesions. In their Discussion, the authors state that nevoid melanomas do not show maturation but examples, that most closely resemble common nevi (and commonly are associated with a remnant of a common nevus), do show maturation. The authors discuss “Spitz nevus-like malignant melanoma.” They discuss patterns of growth at the advancing margin; they document controversial opinions without placing themselves in the controversy. The fact is that classic Spitz “nevi” most commonly show maturation. In addition, if they extend into the reticular dermis, they infiltrate it at the advancing margin. By merely repeating the controversy, little is gained. The authors, in their verbal stores, seem to have a choice of only nevi and melanomas - in the manner of AB Ackerman.
Much of the current controversy regarding the nature of Spitz lesions resides in the designation, “nevus.” Spitz’s lesion is not a nevus; it is a true neoplasm with potential for progressive local growth. It generally lacks the distinguishing characteristics of a common melanocytic nevus. Sophie Spitz characterized the lesions as juvenile melanoma; perhaps if we return to such a designation, order could be restored to the category. Kamino bodies probably are a hodge-podge of structures. When present they favor the Spitz category, but do not establish the representative lesion as a nevus.
A statement that the reexamination of case collections retrospectively for the purpose of publication results in tautologies is credited to Barnhill. A statement that “the notion of metastasizing Spitz’s nevus is illogical and without foundation” is credited to AB Ackerman, et al. The authors (Am J Surg Pathol 26:47, 2002) then state that “a positive lymph node can be assumed as evidence for the malignant potential of a tumor.”
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