MDM II 10

a. 

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characterized by loosely spaced nests of atypical cells with a lymphoid stroma, it may be impossible to make a distinction between a variant of halo nevus, and a MDM of halo nevus-like type.

Halo nevi have a life history. Rarely, an example is encountered in which the population of dermal nevus cells shows uniform, mild atypia (nuclear hyperchromatism) but lymphoid infiltrates are minimal and spotty. In such examples, it is tempting to propose that the nuclear atypism is a marker for a neoplastic transformation which is independent of the qualities which correlate with the development of lymphoid infiltrates (i.e., a neoplastic transformation in which “self” antigens are exposed may precede the appearance of the lymphoid reaction). In fully developed lesions, the lymphoid infiltrates are band-like, and lymphoid cells and histiocytes intermingle among the atypical nevus cells in the dermal nests (i.e., tumor infiltrating lymphocytes). Rarely, histiocytes cluster to form small granulomata. Eosinophils and plasma cells may be a feature. Mitoses may be found in the dermal component.

Of the proposed variants of melanoma, MDM of the halo nevus type has the greatest relevancy to thin MDM in the setting of the premalignant melanocytic dysplasia- melanoma sequence. It is recognized most often as a thin lesion in prognostic category I (i.e., lesions whose vertical growth component measures less than 1 mm in vertical dimensions). With size and number of nests of cells as criteria for the recognition of a vertical growth component, MDM of halo nevus-like type often qualifies as a thin, borderline lesion (e.g., these small, thin lesions may show only 10 or fewer nests of cells in the vertical growth component on a single histologic section). A radial component, that manifests many of the features of a premalignant melanocytic dysplasia (e.g., a lesion of the type that might be encountered in the setting of the dysplastic nevus syndrome) is common; if represented in the epidermis beyond the confines of the dermal component, then the respective lesion qualifies as MDM arising in atypical halo nevus. Atypical halo nevi may be lentiginous and junctional, or compound. It might be appropriate to characterize some lesions as atypical halo nevus of the dermal type on the basis of cytologic atypia in the dermal component in the absence of lentiginous and junctional components.

Often in the vertical growth component of MDM of halo nevus-like type, the cells form closely clustered nests and fascicles, but occasionally are arranged in patternless sheets. In most examples, the degree of cytologic atypia is moderate (i.e., the cells are cytologically minimally deviant). In vertical growth, the neoplastic cells are often bland and spindle shaped, but some examples are composed of small, round cells that have small, round nuclei, marginated chromatin, and a relatively prominent central, acidophilic nucleolus. Large epithelioid cells are occasionally manifested in vertical growth components. The cells of any remnant of a preexisting halo nevus are usually round cells. They tend to vary in size, and to show variation in nuclear size and staining. They are, however, arranged in patterns which are recognizable as variations of those of nevi, and are associated with the lymphoid infiltrates of halo nevus-like phenomena (tumor infiltrating lymphocytes) .

A MDM of halo nevus-like type with radial spread of cells in the epidermis away from the dermal component is characterized as an atypical MDM of halo nevus-like type - a lesion that would appear to have had its origin in an halo nevus.

In some examples of MDM of halo nevus type, the lymphoid infiltrates which characterize halo nevus are also manifested in the vertical growth component. In other examples, the vertical growth component is distinguished by a marked reduction in the intensity of the lymphoid response, if comparison are made with those of the adjacent remnant of halo nevus.

There is no limit on the dimension of the vertical growth component of minimal deviation melanoma of halo nevus type. Examples measuring more than 1.5 mm in vertical dimension are recognizable, but are likely to show severe atypia in vertical growth. In lesions greater than 1 mm in vertical dimensions, most observers would probably ignore the markers for a remnant of a halo nevus; "thicker" examples of this variant are likely to be dismissed as a common melanoma.

MDMs of halo nevus type often are minimally deviant and, by some criteria, might be assigned to the category of "nevoid" melanoma. From the available data, progressive disease is unlikely, if the lesion falls within the limits defined for lesions of prognostic category I. Thin MDM of halo nevus type are evaluated by the same criteria as thin MDM in the setting of the dysplastic nevus syndrome. In addition, they usually are examples of borderline neoplasia of indeterminate malignant potential (thin melanoma of halo nevus type) .

Minimal deviation melanoma of the halo nevus type shares many features with common premalignant dysplasias, and even with related thin, typical melanomas as seen in the setting of dysplastic nevi. Cytologic features are not the chief characteristic. MDMs of halo nevus type are distinguished by the halo nevus phenomena, and usually by the thickness of its vertical growth component (height along the vertical axis of vertical growth component). They are usually minimally deviant in regard to nuclear grades (usually low to intermediate grade), and in regard to usual physical dimensions (i.e., less than 1 mm in vertical dimensions). They qualify as melanocytic neoplasia of indeterminate malignant potential (halo nevus type). In this characterization, size, low to intermediate nuclear grades, and tumor infiltrating lymphocytes are all favorable prognostic findings. The vertical growth component itself is often, but not invariably, free of tumor infiltrating lymphocytes.

Halo-nevus like reactions are common at the deep margin of the vertical growth component of fully evolved melanomas, but such patterns are usually ignored. On the other hand, small, poorly developed vertical growth-like patterns are occasionally encountered as a regional variation in what is otherwise a halo nevus. A relative lack of tumor infiltrating lymphocytes in most vertical growth components of the halo nevus variants facilitates the identification of a small vertical growth component (i.e., one at the very limits of what might be characterized as the minimal number of clustered nests to qualify as vertical growth) In these diverse settings, the implications of the distinctive patterns of immune response are the same as those in halo nevus: the patterns are an expression of cell mediated immunity with the target cells being neoplastic melanocytes.

Regression in the dermal component of both halo nevus and MDM of halo nevus-like type is first heralded by a reduction in the density of the lymphoid infiltrates, and by the appearance of irregular and coarse, hyaline lamellae among small nests of atypical cells, and even among individual "nevus" cells. In late stages, the papillary dermis may be widened and fibrotic; it may be relatively free of nevus cells in either the dermis or the epidermis. In some examples showing prominent regression, nodular lymphoid infiltrates with a high component of histiocytes fill the widened papillary dermis, with only a few junctional or dermal nests as the only surviving marker of the primary process. Fully developed patterns of regression in halo nevi may differ little from those of regressed halo nevus-like melanoma. In such lesions, the nature of the original process cannot be predicted from a histologic evaluation of the residua of immune mediated regression.

Regressing halo nevus-like melanoma is a variation of the patterns seen in MDM of halo nevus type. In the regressing forms, only an rounded nodule of vertical growth with prominent lymphoid infiltrates may be represented as a marker of the regressing vertical growth component. Often, the neighboring epidermis shows effacement of rete ridges and the neighboring papillary dermis is widened, free of tumor, and variably inflamed. Melanophages may not be a feature of the widened papillary dermis. The tumor cells of the vertical growth component tend to be enlarged, and show the dense, nuclear hyperchromasia often manifested in the cells of the dermal component of a typical halo nevus. These lesions may be misdiagnosed as regressing halo nevi, or as regressing melanomas. This type of lesion may lead to charges of malpractice, if later associated with metastases. It probably is related to MDM of halo nevus type, but is unlikely to be characterized as such due to the poor acceptance of the concept of MDM of halo nevus type.

Genital nevi, atypical genital nevi, and related melanomas:

Nevi of the genital and perineal regions commonly are manifested in compound patterns; the junctional nests commonly are large in comparison with similar patterns in other sites in comparable age groups. The genital nevus is commonly removed during the child bearing period of a woman's life. Similar lesions occur in men, but are less commonly excised. The atypical genital nevus shows lentiginous and junctional, or lentiginous and compound, patterns in which the cells manifest varying degrees of atypia. Generally the junctional nests are larger than those of the dysplastic nevi of other anatomic sites. These lesions are characterized by markers for host immune response; some examples may show scattered mitotic figures even in the population of "common" nevus cells in the deeper portion of the dermis. MDM of genital nevus type shows, in addition to the features listed for atypical genital nevus, the patterns of a vertical growth component. In short, the genital nevus and its neoplastic variations are evaluated by the same criteria as the typical nevi and their neoplastic variations. The genital nevus is not in itself a marker for the dysplastic nevus syndrome. It appears to be an expression of exquisite sensitivity of nevus cells to a particular anatomic site.

Spindle Cell Nevi and Melanomas: Although typical melanomas, in the setting of the dysplastic nevus syndrome, commonly show a variety of cell types, including components of spindle cells, some variants are likely to be preponderantly spindle cell in character. Lentigo maligna melanoma and acral lentiginous melanoma are examples. Many of the nevi are also preponderantly spindle (dendritic) cell neoplasms. There is some utility in providing separate recognition for spindle cell categories.

The category of the spindle (and dendritic) cell nevi is heterogeneous. It includes: 1) Spitz nevus, 2) blue nevus (including nevus of Ota and Ito [dermal melanocytoses]) , 3) combined nevus (including blue nevus type, common [deep penetrating] type, and Spitz type), 4) pigmented spindle cell nevus of deep penetrating (dermal) type, 5) cellular blue nevus, 6) pigmented spindle cell nevus of Reed, and (7) epithelioid blue nevus. In this grouping, it is recognized that some Spitz nevi are melanotic, and that deep penetrating nevus is a variant of combined nevus of the common type.

Spindle cell melanomas tend to be internally fasciculated; many are peculiarly related to prominent lentiginous qualities in the overlying epidermis. These lesions are classifiable by attention to cytologic features in the dermal components. Many spindle cell melanomas tend to be loosely fasciculated in vertical growth: they are manifested in patterns of variant vertical growth.

Spitz variant: Spindle cell “nevus” of the Spitz type is exceptional, it is distinctive in comparison with most other variant "nevi." It evolves, and grows rapidly. It is usually amelanotic and the clinical impression often is angioma. Of all the nevi, the quality of "maturation" has been most emphasized in nevus of the Spitz type.

Spitz nevus-like qualities: In general, the cells of Spitz nevus-like variants are epithelioid (plump with abundant cytoplasm) at the dermal-epidermal interface, mostly amelanotic, and both spindle shaped and polygonal or rounded. Herein, as an economy, the Spitz nevus-like variants will be assigned to a spindle cell category. This approach finds justification in the many qualities shared with other spindle cell nevi and melanomas.

A wide range of cytologic features have been acceptable in the Spitz category; this reflects the individuality that is expressed in histologic diagnoses in the face of poorly documented criteria. At the dermal-epidermal interface of typical examples, the cells have plump, round or oval nuclei, prominent nucleoli, and delicate and marginated nuclear chromatin. Nuclear membranes are thin and sharply defined.

Some Spitz nevus-like lesions show atypia in nests at the dermal-epidermal interface with lentiginous and junctional spread away from a more characteristic dermal component. Lesions of the latter type generally are associated with papillary dermal fibrosis (often in lamellar patterns) and with perivascular lymphoid infiltrates in the dermis beneath the lentiginous and junctional components. Such lesions qualify as "atypical spindle cell nevi of the Spitz type."

In other examples, centrally at the dermal-epidermal junction, and in the dermis, the degree of atypia is worrisome, and tumor cells are arranged in broad fascicles. Mitotic activity, including atypical figures, are additional features. Maturation at the deep margin may not be a feature. Such lesions, usually are relegated to the category of either malignant melanoma, or alternately to the category of Spitz nevus-like lesions. If such lesions are truly “nevi,” then it is disturbing that no other "nevus" manifests such variable features. The atypia in some examples is extreme, and the cytologic features often are polymorphic.

Currently, in the Spitz category, a wide range of cytologic and histologic patterns is acceptable. A wedge shaped configuration (overall contour) with the base abutting upon the epidermis, and maturation from the superficial to the deep margin are basic features to search for in a "pattern analysis" of a Spitz “nevus.” In the most typical pattern, broad fascicles of spindle (and epithelioid) cells "rain down" into the dermis from the dermal-epidermal interface. The epidermis is hyperplastic with elongated rete ridges. The papillary dermis near the dermal­epidermal interface is edematous and its vessels are ectatic. In the most characteristic patterns, spindle shaped cells with plump, round to oval nuclei form fascicles near the dermal­epidermal interface. Pale acidophilic bodies are common near the dermal-epidermal interface. Fascicles at the dermal-epidermal interface tend to separate from the epidermis with the formation of clefts. Mitoses are common; they have been observed to be more frequent in superficial portions. Junctional, and dermal, variants have been described. Some of the patterns in the dermal variants are sclerotic. Nerve sheath and lymphatic invasion are acceptable, if all the other features are characteristic. Fascicles of neoplastic cells tend to be more densely spaced in follicular sheaths; in close aggregates, they form bulbous expansions which push into the subcutaneous fat from the confines of an expanded perifollicular sheath.

The concept of immunostimulation, and the significance of a locus for the elaboration of growth factors have application in an evaluation of patterns in nevus of the Spitz type. In the latter setting, the locus for the elaboration of growth factors would be the epidermis and the stroma near the dermal-epidermal interface. The gradient would be depth dependent so that, at a certain level away from the epidermis, the cells would be remote from the locus, and would relinquish the cytologic features which distinguish an immunostimulated cell. From this perspective, could a Spitz nevus be nothing more than a pigmented spindle cell nevus of Reed that has been modified by immunostimulation? There are too many dissimilar features to seriously promote such a proposition but, in practice, there are occasional examples of pigmented spindle cell “nevus” of Reed in which Spitz-like components are also recognizable (a variant of combined nevus?). 

The following designations have application in the manipulation of images in the Spitz category:

1. atypical Spitz nevus (melanocytic dysplasia of Spitz type)

2. MDM of Spitz type (including metastasizing Spitz nevus)

    a. variant vertical growth patterns (patterns basically those of atypical Spitz nevus)

    b. typical vertical growth

3. melanoma with Spitz nevus-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 Spitz nevus- like lesions with "vertical growth components" to a category of borderline neoplasia of Spitz 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.

Most "junctional" Spitz nevi are asymmetrical and are associated with markers for host immune response. At the level of the scanning lens, such lesions are most likely to be initially interpreted as a premalignant melanocytic dysplasia. Most of these lesions appear to be variants of premalignant melanocytic dysplasias; they appear to be independent of classic Spitz nevi (i.e., no remnants of a classic Spitz nevus would be represented in the adjacent dermis) .

In giving recognition to patterns of melanocytic dysplasia and vertical growth, the proposition that an "atypical Spitz nevus," if undisturbed, might evolve into MDM of Spitz nevus-like type would seem to be a valid option. From this perspective, certain minimal deviation melanomas of Spitz type would have evolved in the setting of a unique premalignant dysplasia, and the uniqueness would be evident in atypical cytologic features of Spitz type.

Atypical spindle cell “nevus” of Spitz type is generally a "thin" lesion. Some examples are associated with a dermal component centrally and, in some of these lesions, cellular atypia may be manifested in the dermal component. By the criteria defined for the interpretation of both common minimal deviation melanomas in the setting of multiple dysplastic nevi, and minimal deviation melanoma of halo nevus type, it would seem reasonable to assign these thin, atypical Spitz lesions, with patterns of "variant vertical growth," in the dermis as minimal deviation melanomas. If, however, these lesions are assigned to a category of borderline neoplasia of Spitz type, the need to make the arbitrary assignment of a problematic lesion to a category of either dys- plasia, or melanoma, is avoided. If some reinforcement of this proposed assignment is required, the lesion might then be evaluated by Breslow's criteria. If the lesion is thin, then the assignment of the lesion to the category of borderline melanocytic neoplasia will carry with it therapeutic guidelines that protect both the patient and the physicians. For a lesion as poorly defined as MDM of the Spitz type, even thicker lesions might be assigned to the borderline category.

The concept of minimal deviation melanoma of the Spitz nevus-like type introduces parameters which deviate from those of both the thin common melanomas, and MDM of the halo nevus type. The new parameters include worrisome, cytologic atypia, and even mitotic activity of a degree which, if represented in a common melanoma, would strongly favor a malignant neoplasm (even atypical mitoses are sometimes encountered). By custom in current practice, atypia in Spitz nevus-like variants is accommodated by simply dismissing it, if it is identified in a setting that, overall, has Spitz nevus-like qualities. Finally, in the most characteristic examples (MDM of Spitz type), focal aberrant nesting patterns result in the formation of a nodular component in which coarse fascicles of large atypical cells are clustered (in all aspects satisfying the criteria for the recognition of a vertical growth component). In the dermis adjacent to such a nodule, patterns of more typical Spitz nevus are often preserved. When Spitz nevus-like patterns are preserved at the margin, their presence in combination with a nodular, atypical component make a strong case for the interpretation of the nodular component as a marker for neoplastic transformations leading from a preexisting typical or even atypical Spitz “nevus” to MDM.

Lymphoid infiltrates in some examples of Spitz nevus-like lesions are marked, they have halo nevus-like qualities (tumor infiltrating lymphocytes, or halo nevus phenomena). Mitoses are fairly common in typical Spitz “nevi,” but in atypical nodular variants (MDM of Spitz type), even bizarre mitotic figures may be encountered. Nerve sheath, and/or vascular, invasion may also be features, but are occasional features of otherwise typical Spitz “nevi.”

The concepts of variant, and typical, vertical growth have application in the definition of MDM of Spitz type. The concept of MDM of Spitz type should include examples with variant, as well as typical, vertical growth.

In the concept of MDM, the primacy of both vertical growth (herein, a vertical growth component is the prime requisite for the definition of melanoma), and cytologic atypia have been given recognition in the definition of MDM of the Spitz type. In such lesions, an identification of a remnant showing the pattern of a typical nevus of the Spitz type is a significant aid in the identification of the classic Spitz variant of MDM (transformed MDM). It provides a control with which the patterns and cytologic features in an adjacent compact nodule (i.e., vertical growth component) can be compared. Such a comparison of the patterns will usually provide an identification 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 nodule may be coarse, and usually will be 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 these virtual images, variable patterns and cytologic details - details that otherwise might have to be dismissed as inconsequential - can be molded into those of MDM, or those of a borderline melanocytic neoplasm of indeterminate (or indecisive) malignant potential (Spitz variant) (i.e., transformed into relevant virtual images but not clearly defining the malignant potential).

In current practice, nodules in Spitz nevus-like lesions with cytologic disparity, cytologic atypia, atypical mitoses, and abnormal patterns of aggregation of nests of cells are either accommodated by most pathologists in their definition of Spitz “nevus,” or lesions displaying these features are mistakenly assigned to the default category of typical melanomas. Currently, an expansile nodule that 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 type) is likely to be assigned to the category of Spitz “nevus” without appended qualifications. A similar nodule of atypical cells but with no remnant of classic Spitz nevus in the adjacent dermis (de novo MDM of Spitz type) is likely to be dismissed as a typical melanoma. In view of the infrequent encounters with, and the poor documentation of, the biologic potential 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 then 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 an innocuous 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 in the most typical type of Spitz “nevus.” Some of the metastasizing lesions satisfy the criteria for the recognition of MDM of the Spitz type, and with few, if any, exceptions, metastasizing Spitz “nevus” is either MDM of the Spitz type, or a more aggressive melanoma masquerading in Spitz-like patterns (i.e., a high grade fasciculated, spindle cell, variant vertical growth melanoma - as sometimes encountered in the setting of lentigo maligna melanoma or acral lentiginous melanoma). Some examples are associated with a population of common nevus cells; on the basis of combined patterns such lesions might also qualify as MDM of the combined nevus type. Some of the latter have behaved in the fashion of true melanomas with widespread metastases.

As an example of the arbitrary assignment of a problematic lesion with Spitz nevus- like qualities, a lesion, originally having been assigned to a Spitz nevus-like category, if subsequently found to be associated with regional nodal metastases, is likely, in retrospect, to be reassigned to the category of "metastasizing Spitz nevus;" the deviant histologic features are likely to be dismissed as being within the spectrum of Spitz “nevus,” and the metastasis as "benign." The other likely option is to ignore the Spitz nevus-like qualities and to reassign the lesion to a category of common (typical) melanoma, or to characterize the lesion as "Spitz nevus-like" (Spitzoid) melanoma.

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 (de novo MDM of Spitz type). In these extensions, care must be exercised. Some lentiginous melanomas, including some examples of ALM and LMM - in both of which the vertical growth component can be composed of plump spindle cells - have qualities which might be confused with those of MDM of the Spitz type. Such lesions cannot be easily, and comfortably, assigned to either category. As an option, they could be assigned to a category of melanoma, as indecisive type, but would not be accessible for prognostic evaluations by Breslow's criteria. If such a lesion has metastasized, it is likely to be characterized as either "Spitz nevus-like" melanoma or "metastasizing Spitz nevus."

Similar scenarios can be developed for problematic lesions in the category of combined nevus. All these scenarios find promotion by various experts in the contentions elaborated in malpractice proceedings. In these shenanigans, the force of personalities of experts tend to overshadow the ambiguities in the contentions.

In regard to prognostications by histologic evaluations, MDM of the Spitz type is exceptional. 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 as melanoma, deviates from the 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 melanoma: MDM of the Spitz nevus- like type is an example. 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 nevus-like type. Time has confirmed this wisdom. In fact, some of the "metastasizing Spitz “nevi” (MDM of the Spitz 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 an otherwise benign fashion. As an alternative, these lesions might be characterized as melanocytic neoplasia of indeterminate malignant potential (Spitz 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, but complete, 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 more controversy. There would be no uniformity and no basis for inter-observer agreement. There would be considerable freedom for the manipulation of clinical data, diagnoses, and linguistics by trial lawyers.

Pigmented spindle cell nevi: The category of pigmented spindle cell nevi 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 both combined nevus, and deep penetrating nevus are lesions with more significant dimensions: they are closely related and are sometimes 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." It 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, and 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........

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