Atypical genital nevi. A clinicopathologic analysis of 56 cases

Atypical genital nevi are rare melanocytic lesions that most commonly arise on the vulva of young women. They are currently regarded as nevi of special sites, in that despite histologically worrisome features, their clinical behavior is reportedly benign. However, only few studies with limited follow-up data are available. To better characterize the clinical presentation and behavior of these lesions and to further delineate their histologic features, we retrieved 56 atypical genital nevi arising in the lower female genital tract from our departmental and consultation files. The 56 lesions arose in 55 female patients with a median age of 26 years (range, 6 to 54 y). The dominant histologic feature was a lentiginous and nested junctional component composed of prominent round or fusiform nests, which often showed retraction artifact and/or cellular dyscohesion. Cytologic atypia was mild in 11 cases (20%), moderate in 34 (60%), and severe in 11 (20%). Ten cases (18%) showed focal pagetoid spread, with extension to the granular layer and stratum corneum in 1 case. The atypical junctional melanocytic proliferation was associated with a large common dermal nevus component that dominated the lesion in 26 cases (46%). Adnexal spread (46%) and nuclear atypia of melanocytes situated in the superficial dermis (39%) were relatively common, but dermal mitoses (7%) were uncommon and maturation was present in all cases. A broad zone of dense eosinophilic fibrosis within the superficial dermis was a frequent finding (41%). Clinical follow-up was available in 45 cases (80%) with a median follow-up period of 3.5 years (range, 1 to 16 y). Only 1 lesion recurred, 1.5 years after the initial excision. The original nevus in this patient had only mild cytologic atypia and was present at the margins of excision. The recurrent/persistent nevus was reexcised, and there was no further clinical recurrence in 11.5 additional years of follow-up. Our data support the hypothesis that atypical genital nevi have a benign clinical course despite their occasionally striking cytologic and architectural atypia. Awareness and recognition of this group of melanocytic lesions is important to avoid over diagnosis as melanoma with subsequent wide excision and possibly sentinel lymph node biopsy.     

Analysis of mutations in B-RAF, N-RAS, and H-RAS genes in the differential diagnosis of Spitz nevus and spitzoid melanoma

A definite diagnosis cannot be established based on histologic features alone in a large number of Spitz nevi and spitzoid melanomas. In a vast majority of common benign and malignant melanocytic lesions, B-RAF and N-RAS mutations were described, but these were not detected in Spitz nevi. In contrast, H-RAS mutations were frequently encountered in Spitz nevi, but only rarely in melanomas. To date, B-RAF mutation analysis has not been reported in atypical Spitz nevi, and there are only a few reports of it in spitzoid melanomas. We analyzed 96 formalin-fixed, paraffin-embedded spitzoid melanocytic lesions for hotspot mutations in B-RAF, N-RAS, and H-RAS genes to test the assumption whether mutation analysis would assist a more accurate diagnosis of spitzoid melanocytic lesions, which are notoriously difficult to classify. B-RAF or N-RAS mutations were observed in 31 of 36 (86%) spitzoid melanomas, and in 6 of 7 (86%) spitzoid melanoma metastases. In contrast, none of the 14 Spitz nevi and none of the 16 atypical Spitz nevi had mutations in any of the three genes. A B-RAF or N-RAS mutation was found in 8 of 23 (35%) spitzoid lesions suspected for melanoma. H-RAS mutations were detected in 4 of 14 (29%) Spitz nevi, in 3 of 22 (14%) atypical Spitz nevi, in 1 of 15 (7%) spitzoid tumors suspected for melanoma, but in none of the spitzoid melanomas. These results strongly indicate that Spitz nevi and spitzoid melanomas are genetically unrelated entities. Furthermore, we can conclude that mutation analysis may be useful as an additional diagnostic tool to distinguish between benign and malignant spitzoid lesions.     

Desmoplastic (sclerotic) nevus: an underrecognized entity that resembles dermatofibroma and desmoplastic melanoma.

Desmoplastic (sclerotic) nevus, a benign melanocytic neoplasm characterized by predominantly spindle-shaped nevus cells within a fibrotic stroma, can be confused with fibrous lesions and other melanocytic proliferations, including desmoplastic melanoma. We compared the histologic and immunohistochemical features of 16 desmoplastic nevi, nine desmoplastic melanomas, four hypopigmented blue nevi, and six dermatofibromas. The similarities between desmoplastic nevi and dermatofibromas included epidermal hyperplasia (12 of 16), presence of keloidal collagen (15 of 16), hypercellularity (16 of 16), and increased numbers of factor XIIIa-positive dendritic cells (12 of 12). The absence of adnexal induction (0 of 16), the rarity of lesions with multinucleated cells (3 of 16) or epidermal hyperpigmentation (2 of 16), and the presence of S-100 immunoreactivity (16 of 16) and melanocytic proliferation (9 of 16) helped differentiate desmoplastic nevi from dermatofibromas. The similarities between desmoplastic nevi and desmoplastic melanomas included the presence of atypical cells (16 of 16) and HMB-45 expression in the superficial portion of the lesions (11 of 16). The infrequent location on the head or neck (1 of 16), the absence of mitotic figures (0 of 16), a significantly lower number of Ki-67-reactive cells, and a decrease in HMB-45 expression in the deep area of the lesions (8 of 11) helped distinguish desmoplastic nevi from desmoplastic melanoma. Desmoplastic nevi had overlapping features with hypopigmented blue nevi, but features tending to favor the latter included a predominance of ovoid nuclei, higher numbers of atypical cells, and homogeneous staining with HMB-45. We conclude that a combination of histologic and immunohistochemical criteria facilitates the reliable diagnosis of desmoplastic nevus from its simulators.     

HMB-45 staining of dysplastic nevi. Support for a spectrum of progression toward melanoma

Dysplastic nevi are melanocytic tumors that occupy intermediate positions in the spectrum of melanocytic proliferations. Although they are invariably cured if completely excised, their biologic potential if left untreated is unknown. We examined a series of such lesions with HMB-45, a melanocyte-specific antibody, in order to explore protein expression within these borderline lesions. HMB-45 has previously been shown to label intraepidermal melanocytes within melanomas and within all nevi. Intradermal melanoma cells also label with HMB-45, but dermal nevus cells within common melanocytic nevi do not normally stain. In contrast, we found mild to moderate staining of nevus cells within the papillary dermis of dysplastic nevi and within residual nevus cells adjacent to malignant melanomas. In the same lesions, we demonstrated strong staining of intraepidermal melanocytes. Thus, dermal nevus cells within dysplastic nevi and within residual nevus cells adjacent to malignant melanomas are expressing low-level amounts of a protein expressed by melanoma cells, but not by dermal nevus cells within wholly benign melanocytic tumors. This lends support to the concept of these lesions as precursor lesions with undetermined biologic potential.     

Proliferative nodules arising within congenital melanocytic nevi: a histologic, immunohistochemical, and molecular analyses of 43 cases

The histopathologic interpretation of proliferative nodules (PNs) in congenital melanocytic nevi can present significant challenges as some PNs may exhibit atypical features that make the distinction from melanoma difficult. We compared histologic features, Ki-67%, PHH3, and CD117% expression levels by immunohistochemistry in 18 benign and 25 atypical PNs (from 41 patients) with that of background congenital nevi (of these 43 cases), 10 congenital nevi, and 3 dermal melanomas arising in congenital melanocytic lesions. In addition, we evaluated the presence of BRAF, GNAQ, HRAS, KRAS, and NRAS mutations in all groups using the SNaPshot Multiplex System. Follow-up was available on 19 patients (9 benign and 10 atypical PNs) (range, 2 to 20 y; median, 8 y) and all were alive with no evidence of disease. The specific histologic features of atypical PNs, such as sharp demarcation (P<0.001), expansile growth (P<0.001), epidermal effacement (P<0.001), nuclear pleomorphism (P<0.001), and increased mitoses (P<0.001), differed significantly from those of benign PNs. Immunohistochemical results showed that Ki-67% and PHH3 scores, but not CD117% expression, were significantly higher (P<0.05) in atypical PNs. Molecular analyses showed that the PNs and background congenital melanocytic nevi of the giant congenital nevi possess more frequent NRAS mutations and infrequent BRAF mutations when compared with those of the remaining cases. These findings suggest that histologic features and Ki-67 and PHH3 expression levels are the strongest parameters to distinguish between benign versus atypical PNs. The immunohistochemical results suggest that atypical PNs are distinct borderline lesions residing between benign PNs and dermal melanomas. Although numerous mutations are detected in the samples, the diagnostic use of molecular analysis in this regard is limited.     

Low-risk and high-risk histologic features in conjunctival primary acquired melanosis with atypia: Clinicopathologic analysis of 29 cases

The current World Health Organization classification of conjunctival melanocytic proliferations divides them into conjunctival nevi and invasive melanoma but, in contrast to other anatomic sites, does not recognize melanoma in situ. All atypical intraepithelial conjunctival proliferations are included in a heterogeneous category designated as primary acquired melanosis (PAM) with atypia. We performed clinicopathologic analysis of 29 cases of PAM with atypia. On the basis of histologic features and frequency of association with invasive melanoma and metastases, we were able to divide our cases into 2 histologic groups. The low-risk group (13 cases) included lesions composed of small to medium size melanocytes with high nuclear to cytoplasmic ratio and small to medium size hyperchromatic nuclei devoid of nucleoli showing predominantly single cell lentiginous growth pattern. Invasive melanoma occurred in only 2 cases from this group. None of these lesions metastasized. The second, high-risk group (16 cases), showed increased frequency of association with invasive melanoma (15/16 cases, 94%) and metastases (4/16 cases, 25%). These lesions were more heterogeneous architecturally but were all composed of melanocytes showing various degrees of epithelioid features such as abundant cytoplasm, vesicular nuclei, or prominent nucleoli. In 4 cases discrete areas showing high-risk and low-risk features were identified. All 4 lesions were associated with invasion. Our findings offer a practical approach for prognostically useful subclassification of PAM with atypia, which emphasizes cytologic features of intraepithelial conjunctival melanocytic proliferation.     

Genomic analysis of blue nevi and related dermal melanocytic proliferations

Blue nevi are benign dermal melanocytic proliferations that can sometimes share overlapping microscopic features with melanoma. We used comparative genomic hybridization to analyze three groups of dermal melanocytic proliferations. Group 1 consisted of 10 cellular blue nevi and 1 deep penetrating nevus, none of which showed chromosomal aberrations. Group 2 consisted of 11 lesions that were histopathologically ambiguous. Three of these lesions demonstrated chromosomal aberrations (three or fewer per lesion). Group 3 consisted of seven histopathologically malignant lesions, each showing three or more chromosomal aberrations. Moderate to severe cytologic atypia and a mitotic rate of three or more mitoses per 10 high power fields were present in six of eight (75%) lesions that had at least three chromosomal aberrations but were absent in 15 of 20 (75%) lesions without chromosomal aberrations. Necrosis was present in four of the 29 (13%) lesions, with every lesion with necrosis demonstrating three or more genomic abnormalities. In conclusion, histopathologically unequivocally benign or malignant dermal melanocytic proliferations show nonoverlapping patterns of chromosomal aberrations. Ambiguous lesions can be separated into lesions with and without chromosomal aberrations. Future studies with clinical follow-up are necessary to determine which aberrations are most informative for classification of these lesions.     

Histologic classification of the combined nevus. Analysis of the variable expression of melanocytic nevi.

The designation combined nevus gives recognition to mixed cytologic patterns. In the common variant, plump, pigmented spindle cells form fascicles among nests of ordinary nevus cells. In other variants, one or several cellular components that share cytologic features with either a blue nevus or a Spitz nevus are represented. Ninety-five cases, 49% of which were of the common type, were studied. Grossly, most of the lesions were darkly pigmented papules or nodules. The clinical diagnosis in three-fourths of the cases was nevus, blue nevus, or melanoma. Fifteen percent had concomitant histologic features of melanocytic dysplasia, and most of these lesions were of the common type. For the common variant, the cytologic features, pattern of apparent infiltration, and variable representation of the features of a premalignant melanocytic dysplasia often mislead a pathologist in interpreting and predicting biologic potential. In combined nevi, the phenotypic diversity and genetic lability of melanocytic nevus cells is manifested.     

Melanocytic nevi with an atypical epithelioid cell component: clinical, histopathologic, and fluorescence in situ hybridization findings

Combined melanocytic nevi can contain a phenotypically distinct population of large atypical epithelioid cells in a background of smaller banal-appearing melanocytes. On the basis of the pattern of proliferation and degree of pigmentation, nevi with this pattern have been referred to as nevi with an atypical epithelioid cell component (N-AECC). When N-AECC display sheet-like or an expansile nodular growth pattern, notable cytologic atypia, and any level of mitotic activity, they can be difficult to distinguish from melanoma. The clinical history and appearance of these lesions may similarly raise concern for melanoma. In view of this diagnostic problem, we present 28 cases of N-AECC from our dermatopathology consultation and in-house practice. All 28 cases were found to be negative on the basis of fluorescence in situ hybridization (FISH) for imbalanced chromosomal aberrations commonly found in melanoma. The clinical outcomes showed a benign clinical course for all cases for which the outcome information was available. FISH analysis also revealed that, in 4 of 28 cases (14%), the AECC of the lesion demonstrated polyploidy localized to the large epithelioid cell component. This is likely more common among cases of N-AECC that have an atypical spitzoid epithelioid cell component, particularly those with obvious senescent nuclear changes. Care must be taken to avoid the pitfall of misinterpreting these FISH findings as changes consistent with melanoma. The use of ancillary testing methods including FISH may be beneficial in improving the diagnostic accuracy involved in making the distinction of N-AECC from melanoma. Further, we report a novel finding of polyploidy seen in certain cases of benign N-AECC.     

Persistent (recurrent) Spitz nevi: a histopathologic, immunohistochemical, and molecular pathologic study of 22 cases

This report describes 22 Spitz nevi that seemed to have been clinically removed but persisted and clinically recurred at the biopsy site. These were evaluated in terms of histopathology, immunohistochemistry, and molecular pathology using comparative genomic hybridization (CGH) and fluorescent in situ hybridization. One of these 22 lesions was originally reported as an atypical melanocytic proliferation with some features of a Spitz nevus and was included in the study set at an early stage but was later recognized as melanoma after metastasis to regional lymph nodes 3 years after the local recurrence. We noted four histopathologic patterns in the recurrent lesions: 1) a predominantly intraepidermal pattern resembling "pseudomelanoma" as seen in recurrent "common" melanocytic nevi, 2) a compound, mostly nested pattern above or within a scar that was nearly identical to the originally biopsied Spitz nevus, 3) a nodular growth pattern that closely simulated invasive melanoma, and 4) a desmoplastic pattern resembling an intradermal desmoplastic Spitz nevus. Although the majority of recurrent lesions exhibited asymmetry and pagetoid spread, the dermal component usually had a low mitotic rate and retained architectural and cytologic maturation, which allowed distinction from invasive melanoma. Except for the metastasizing melanoma, the immunostaining pattern with S-100 and HMB-45 was identical to that previously reported for Spitz nevi. Ki67 revealed a very low proliferation rate in all cases, including the melanoma. CGH performed in 10 cases yielded results consistent with Spitz nevi in eight cases. The remaining two cases showed CGH profiles more typical of melanoma, and one of these was the above-referenced case of melanoma, proven by metastasis. Although ancillary molecular techniques such as CGH are of great help in distinguishing these from melanoma, until such techniques become widely available we advocate complete but conservative excision of any recurrent Spitz nevus.     

Atypical cellular blue nevi (cellular blue nevi with atypical features): lack of consensus for diagnosis and distinction from cellular blue nevi and malignant melanoma ("malignant blue nevus")

The distinction of cellular blue nevi (CBN) with atypical features ["atypical" CBN (ACBN)] from conventional CBN and malignant melanomas related to or derived from CBN remains a difficult problem. Here, we report on the diagnosis of various cellular blue melanocytic neoplasms by 14 dermatopathologists who routinely examine melanocytic lesions. Three parameters were assessed: (1) for between rater analyses, we calculated interobserver agreement by the kappa statistic (regardless of whether the diagnosis was correct). (2) For each individual lesion, we reported whether a majority agreement (>50%) was reached and, if so, whether the majority agreed with the gold standard diagnosis, derived from standardized histopathologic criteria for melanoma, definitive outcome such as metastatic event or death of disease, or disease-free follow-up for > or =4 years. (3) For the individual pathologists, we calculated sensitivity and specificity for each type of lesion. The study set included 26 melanocytic lesions: (1) 6 malignant melanomas developing in or with attributes of CBN; (2) 11 CBN with atypical features and indeterminate biologic potential (ACBN); (3) 8 conventional CBN; and (4) 1 common BN. The kappa values for interrater agreement varied from 0.52 (95% confidence interval 0.45, 0.58) for melanoma to 0.02 (0.05, 0.08) for ACBN and 0.20 (0.13, 0.28) for CBN. The kappa for all lesions was 0.25 (0.22, 0.28). The pathologists' sensitivities were 68.6% (61.0%, 76.1%) for melanoma, 33.1% (21.0%, 45.2%) for ACBN, and 44.6% (29.0%, 60.3%) for CBN. The specificities were 65.7% (55.8%, 75.6%) for melanoma, 84.7% (77.3%, 92.2%) for ACBN, and 89.9% (82.7%, 97.1%) for CBN. Overall, greater than 50% of the pathologists agreed and were correct in their diagnosis 38.5% (10 lesions) of the time. There was a majority agreement, but with an incorrect diagnosis, another 26.9% (7 lesions) of the time. Six of the 7 majority agreements with an incorrect diagnosis were for ACBN lesions. In summary, the results of our study indicate that there is substantial confusion and disagreement among experienced histopathologists about the definitions and biologic nature of cellular blue melanocytic neoplasms particularly those thought to have atypical features ("atypical" CBN).     

Malignant melanoma with paradoxical maturation

Typically, melanocytic nevi "mature" (i.e., exhibit a morphologic shift to smaller or spindle cells with progressive depth in the dermis). In contrast, most malignant melanomas (conventional MMs) lack maturation, and are composed of large pleomorphic cells throughout. The authors describe a series of melanomas with paradoxical maturation mimicking the pattern of nevi. Seventeen primary invasive melanomas with paradoxical maturation (IMPs), two epidermotropic metastatic melanomas with maturation (EMMMs), 13 compound nevi (CN), and 14 conventional MMs without apparent maturation were analyzed by histologic, cytomorphometric, and immunohistochemical techniques. With increasing dermal depth, both CN and IMPs had smaller nuclear and cellular areas, and decreased expression of Ki-67, glycoprotein (gp)100 (with HMB-45), and tyrosinase. IMPs had significant differences from conventional MMs; namely, smaller nuclear and cytoplasmic areas (deep), and decreased expression of Ki-67 (superficial and deep), gp100 (deep), and tyrosinase (deep). IMPs also had notable differences from CN: namely, larger nuclear and cellular areas, more confluence, more mitotic figures, increased Ki-67 and gp100 expression in both the superficial and deep portions, and more melanin (deep). The two EMMMs exhibited histologic and immunohistochemical features similar to the primary IMPs. IMP, because of its mimicry of nevus, can present a diagnostic hazard. The authors propose histologic, morphometric, and immunohistochemical criteria that facilitate recognition and accurate diagnosis of this unusual variant of melanoma.     

Loss of expression of protein kinase a regulatory subunit 1alpha in pigmented epithelioid melanocytoma but not in melanoma or other melanocytic lesions

Pigmented epithelioid melanocytoma (PEM) is a recently described entity comprising most cases previously described as "animal-type melanoma" and epithelioid blue nevus (EBN) occurring in patients with the multiple neoplasia syndrome Carney complex (CNC). Mutations of the protein kinase A regulatory subunit type 1alpha (R1alpha) (coded by the PRKAR1A gene) are found in more than half of CNC patients. In this study, we investigated whether PEM and EBN are related at the molecular level, and whether changes in the PRKAR1A gene status and the expression of the R1alpha protein may be involved in the pathogenesis of PEM and other melanocytic lesions. Histologic analysis of hematoxylin and eosin-stained sections and immunohistochemistry (IHC) with R1alpha antibody were performed on 34 sporadic PEMs, 8 CNC-associated PEMs from patients with known PRKAR1A mutations, 297 benign and malignant melanocytic tumors (127 conventional sections of 10 compound nevi, 10 Spitz nevi, 5 deep-penetrating nevi, 5 blue nevi, 6 cellular blue nevi, 2 malignant blue nevi, 3 lentigo maligna, and 86 melanomas of various types); in addition, 170 tissue microarray sections consisting of 35 benign nevi, 60 primary melanomas, and 75 metastatic melanomas, and 5 equine dermal melanomas, were examined. Histologic diagnoses were based on preexisting pathologic reports and were confirmed for this study. DNA studies [loss of heterozygosity (LOH) for the 17q22-24 locus and the PRKAR1A gene sequencing] were performed on 60 melanomas and 7 PEMs. IHC showed that R1alpha was expressed in all but one core from tissue microarrays (169/170), and in all 127 melanocytic lesions evaluated in conventional sections. By contrast, R1alpha was not expressed in the 8 EBN from patients with CNC and PRKAR1A mutations. Expression of R1alpha was lost in 28 of 34 PEMs (82%). R1alpha was expressed in the 5 equine melanomas studied. DNA studies correlated with IHC findings: there were no PRKAR1A mutations in any of the melanomas studied and the rate of LOH for 17q22-24 was less than 7%; 5 of the 7 PEMs showed extensive 17q22-24 LOH but no PRKAR1A mutations. The results support the concept that PEM is a distinct melanocytic tumor occurring in a sporadic setting and in the context of CNC. They also suggest that PEM differs from melanomas in equine melanotic disease, further arguing that the term animal-type melanoma may be a misnomer for this group of lesions. Loss of expression of R1alpha offers a useful diagnostic test that helps to distinguish PEM from lesions that mimic it histologically.     

Acquired Melanocytic Lesions and the Decision to Excise: Role of Color Variegation and Distribution as Assessed by Dermoscopy

BACKGROUND: Because melanoma may sometimes be difficult to differentiate from nevi with clinical atypia, many benign lesions also undergo surgical removal. OBJECTIVE: To assess color type and distribution in dermoscopic melanocytic lesion images and to analyze the influence of color parameters on the diagnostic process and the decision to excise. METHODS: Overall, 603 images, referring to 112 melanomas and 491 nevi, were retrospectively subdivided into four groups: "clearly benign," "follow-up," "dermoscopic atypical nevi," and "dermoscopic melanomas," according to their dermoscopic aspects. The frequency of color type, number, and asymmetry were evaluated on digital images. RESULTS: With respect to lesions not eligible for excision according to dermoscopy (but excised for cosmetic reasons), those excised with a suspicion of malignancy showed a higher number of colors, whose distribution was also more asymmetric. Moreover, the frequency of the presence of black and blue-gray progressively increased from clearly benign lesions to atypical nevi and dermoscopic melanomas. CONCLUSION: In dermoscopic images, color parameters are essential elements for the diagnosis of atypical nevus, which can be differentiated from both a clearly benign lesion and a melanoma. Furthermore, pigmentation asymmetry and the presence of blue-gray represent the main color features, which should lead to the decision to excise.     

Combined melanocytic nevi: histologic variants and melanoma mimics

Combined melanocytic nevi are composed of 2 or more distinct populations of nevomelanocytes. Most commonly used to describe the combination of blue nevi with common nevi, it may also be applied to other combinations of benign melanocytic proliferations, including Spitz nevi and nevi with deep dermal pigmented nevomelanocytes. We report the incidence and distribution of these tumors at the Massachusetts General Hospital over the past decade and review guidelines for diagnostic criteria and nomenclature. Between 2000 and 2010 we identified 511 cases of combined nevi, represented by 4 histologically distinct diagnostic categories: (1) blue nevus, (2) nevi with deep dermal pigmented nevomelanocytes (plexiform/deep penetrating, inverted type A/clonal), (3) Spitz or pigmented spindled cell nevus, combined with another type of nevus (usually common or dysplastic), and (4) other combinations including 2 or more nevus types. Nearly one fifth of these tumors displayed atypical features; atypia was observed more often in combined nevi with Spitz or deep pigmented elements (26 of 55, 47%, and 25 of 98, 26%, respectively) than in combined common and blue nevi (37 of 336, 11%). Clinical follow-up data were available for 83% of the patients with atypical combined nevi; none developed recurrence or metastasis with a mean follow-up of over 4 years.     

Malignant melanoma, dysplastic melanocytic nevi, and Spitz tumors. Histologic classification and characteristics

The classification and pertinent histopathologic features of cutaneous melanoma, dysplastic melanocytic nevi, and Spitz tumors are presented. A discussion on melanoma emphasizes an objective approach to classification based on histomorphologic features including location in the skin, disposition and frequency of melanocytes, other specific morphologic features, and cell type. Other topics addressed include common and unusual variants of melanoma, the use of immunohistochemistry, and the histopathologic reporting of melanoma.     

Histologic distinction between subungual lentigo and melanoma

The distinction between a benign subungual pigmented macule (lentigo) and an early lesion of melanoma in situ can be difficult. To identify histologic parameters of potential diagnostic value, we retrospectively reviewed biopsies and excisions of 35 pigmented nail lesions. We studied 20 melanomas (10 invasive and 10 noninvasive) and 15 benign subungual melanotic lentigines. Ten specimens of normal nail apparatus obtained for reasons other than melanonychia were also examined as controls. The parameters, which were analyzed, included the density of melanocytes, the presence of multinucleated cells, pagetoid spread, cytologic atypia, inflammation, and the distribution of melanin pigment. The density of melanocytes was measured as the number of cells per 1 mm stretch of subungual dermo-epithelial junction [=melanocyte count (MC)]. The MC for invasive melanomas was as follows: mean=102, median=92.5, and range 52 to 212. For noninvasive (only in situ) melanoma, the mean MC was 58.9, median 51, and range 39 to 136. For benign subungual melanotic macules, the mean MC was 15.3, median 14, and range 5 to 31. In normal controls, the mean MC was 7.7, median 7.5, and range 4 to 9. Qualitative features associated with in situ melanoma and useful for its distinction from benign subungual melanotic macules included the presence of confluent stretches of solitary units of melanocytes, multinucleated melanocytes, lichenoid inflammatory reaction, and florid pagetoid spread of melanocytes.     

Immunohistochemical analysis of novel monoclonal antibody PNL2 and comparison with other melanocyte differentiation markers

PNL2 is a novel monoclonal antibody, which has recently been introduced as an immunohistochemical reagent to stain melanocyte and tumors derived thereof. In the present study, we analyzed the immunoreactivity of this mAb in various normal tissues, melanocytic nevi, primary and metastatic melanoma, nonmelanocytic tumors, including histologic mimickers of melanoma as well as angiomyolipoma, and multiple cell lines derived from different tumors types. We used several tissue microarray panels as well as selected conventional sections from tissue blocks. For metastatic melanoma, immunoreactivity for PNL2 was compared with A103 (Melan-A/MART-1), T311 (tyrosinase), HMB45 (gp100), and D5 (MITF). Positive staining with PNL2 was found in normal melanocytes and neutrophils, but no other normal cell type. Among melanocytic lesions, both benign nevi as well as primary malignant melanomas, especially epithelioid variants thereof, were commonly immunopositive. Only 1 of 13 desmoplastic melanomas reacted with PNL2. PNL2 showed high sensitivity for metastatic melanoma (87%). In comparison, 82% of metastatic melanomas were positive for A103, 76% for HMB45, 92% for T311, and 84% for D5. The combined use of all five reagents minimized the number of immunonegative cases. None of the selected nonmelanocytic tumors (carcinomas or soft tissue neoplasms) was positive for PNL2 in this series except for angiomyolipomas and chronic myeloid leukemias and 1 single case of a malignant peripheral nerve sheath tumor with heterologous differentiation (malignant Triton tumor). Despite its reactivity with neutrophils, PNL2 appears to be a valuable supplementary reagent for the diagnosis of melanocytic tumors.