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Accurate and complete pathology reports are critical for the optimal management of cancer patients. Protocols for the pathologic reporting of Merkel cell carcinoma (MCC) have been developed independently by the Royal College of Pathologists (UK) and the College of American Pathologists. In this study, data elements for pathologic reporting of MCC were analyzed by an international panel of pathologists and clinicians with the aim of developing a common, internationally agreed upon dataset useful for clinical practice. The International Collaboration on Cancer Reporting expert review panel developed a protocol containing “core” (required) and “noncore” (recommended) elements. Core elements were defined as those that had evidentiary support and were unanimously agreed upon by the review panel as essential for the clinical management, staging, and/or assessment of prognosis in patients with MCC. Noncore elements were those considered to be clinical of interest, but with lesser degrees of supportive evidence or nonactionable implications. Ten core data elements for pathology reports on primary MCC were defined. Development and agreement on this evidence-based protocol at an international level was accomplished in a timely and efficient manner. The template developed for melanoma reporting was used as a structural base for this initiative. It is applicable to, and may facilitate the development of, protocols for other tumor types. Widespread utilization of an internationally agreed upon structured pathology dataset for MCC can be expected to lead to improved patient management. It should also facilitate collaborative clinical research.

The distinction of metastatic melanoma from melanocytic nevi in lymph nodes can on occasion be difficult. As diffuse immunohistochemical (IHC) PRAME (PReferentially expressed Antigen in MElanoma) expression is detected in the majority of primary and metastatic melanomas, but rarely in nevi, we reasoned that PRAME could be a useful adjunct marker for the diagnosis of melanocytes in lymph nodes. In this study, we examined 45 nodal melanocytic deposits comprising 30 nodal nevi and 15 melanoma metastases. The latter were diagnostically not straightforward because they either coexisted with nodal nevi or were present in perinodal fibrous tissue. All nodal nevi (30/30) were negative for PRAME, whereas all melanoma metastases (15/15) were diffusely positive for PRAME IHC. We additionally report the novel use of a PRAME/Melan A dual-label immunostain. Our results show that PRAME IHC may be useful in the assessment of diagnostically challenging nodal melanocytic deposits, such as intraparenchymal nodal nevi, metastases confined to the capsular fibrous tissue, or in the setting of small metastases coexisting with a nodal nevus in the same lymph node.

A number of common driver mutations have been identified in melanoma, but other genetic or epigenetic aberrations are also likely to play a role in the pathogenesis of melanoma and present potential therapeutic targets. Translocations of the anaplastic lymphoma kinase (ALK), for example, have been reported in spitzoid melanocytic neoplasms leading to kinase-fusion proteins that result in immunohistochemically detectable ALKexpression. In this study, we sought to determine whether ALKwas also expressed in nonspitzoid primary and metastatic cutaneous melanomas. ALK immunohistochemistry was performed on 603 melanomas (303 primary and 300 metastatic tumors) from 600 patients. ALK immunohistochemistry expression was identified in 7 primary and 9 metastatic tumors. In 5 of 7 primary tumors and in 6 of 9 metastatic lesions, the majority of tumor cells were immunoreactive for ALK. In the other 2 primary and 3 metastatic lesions, positive staining was identified in less than half of the tumor cells. ALK positivity was found in the presence or absence of BRAFor NRASmutations. In contrast to prior observations with ALK-positive Spitz tumors, none of the ALK-positive melanomas harbored a translocation. Instead, the ALK-positive melanomas predominantly expressed the recently described ALKisoform, ALKATI, which lacks the extracellular and transmembrane domains of wild-type ALK, consists primarily of the intracellular tyrosine kinase domain, and originates from an alternative transcriptional initiation site within the ALKgene. The findings are clinically relevant as patients with metastatic melanoma who have ALK expression may potentially benefit from treatment with ALK kinase inhibitors.

Desmoplastic melanoma (DM) is a rare variant of melanoma with distinct clinical, histopathologic, and immunohistochemical features. Clinically, DM differs from conventional melanoma by a higher propensity for local recurrence and less frequent metastatic spread to regional lymph nodes. In its pure form, DM has a distinct appearance displaying a low density of fusiform melanocytes in a collagen-rich matrix. Whereas a number of mutations have been identified in primary melanoma, including BRAF, NRAS, GNAQ, GNA11, and KIT, and the occurrence of these mutations has been found to correlate to some extent with the histopathologic features, anatomic site, and/or mode of sun exposure, no distinct set of mutations has so far been reported for DM. To study the potential association of neurofibromin (NF1) mutations with DM, we examined 15 desmoplastic and 20 non-DMs by next-generation sequencing. Mutations of the NF1gene were found in 14 of 15 (93%) DMs and 4 of 20 (20%) non-DMs. The high frequency of NF1mutations in DMs suggests an important role for NF1 in the biology of this type of melanoma.

Spitz tumors represent a group of melanocytic neoplasms that typically affect young individuals. Microscopically, the lesions are composed of cytologically distinct spindle and epithelioid melanocytes, with a range in the architectural display or the cells, their nuclear features, and secondary epidermal or stromal changes. Recently, kinase fusions have been documented in a subset of Spitz tumors, but there is limited information on the clinical and pathologic features associated with those lesions. Here, we report a series of 17 patients (9 male, 8 female) with spitzoid neoplasms showing ALKfusions (5 Spitz nevi and 12 atypical Spitz tumors). The patients’ ages ranged from 2 years to 35 years (mean=17 y; median=16 y). Most lesions were located on the lower extremities and presented clinically as polypoid nodules. All tumors were compound melanocytic proliferations with a predominant intradermal growth. Tumor thickness ranged from 1.1 to 6 mm (mean=2.9 mm; median=2.5 mm). The most characteristic histopathologic feature of the tumors (seen in all but 2 lesions) was a plexiform dermal growth of intersecting fascicles of fusiform melanocytes. All but 2 tumors were amelanotic. All tumors were strongly immunoreactive for ALK. The ALKrearrangements were confirmed in all cases by fluorescence in situ hybridization (FISH), and the fusion partner was determined by quantitative polymerase chain reaction as TPM3(tropomyosin 3) in 11 cases and DCTN1(dynactin 1) in 6 cases. None of the 8 tumors that were analyzed by FISH for copy number changes of 6p, 6q, 9p, or 11q met criteria for melanoma. Two patients underwent a sentinel lymph node biopsy, and in both cases melanocyte nests were found in the subcapsular sinus of the node. Array comparative genomic hybridization of these 2 tumors revealed no chromosomal gains or losses. In conclusion, our study revealed that Spitz nevitumors with ALKrearrangement show a characteristic plexiform morphology and that ALKimmunohistochemistry and FISH enable the accurate identification of this morphologic and genetic distinct subset of spitzoid neoplasms.

Basal cell carcinosarcoma is a rare biphenotypic malignant skin tumor, in which one tumor component has light microscopic features of basal cell carcinoma, whereas the other has features of sarcoma. Clinical experience with this tumor is limited, and associated molecular genetic alterations are unknown. Herein, we report a unique case of metastatic basal cell carcinosarcoma, in which we analyzed the 2 components of the primary tumor as well as the metastasis by next-generation sequencing. The patient was a 72-year-old man who presented with a 7-year history of a large tumor of the left forearm. The tumor showed mixed features of basal cell carcinoma and undifferentiated sarcoma. The patient underwent a wide local excision and sentinel lymph node biopsy, which revealed microscopic subcapsular deposits of metastatic sarcomatoid tumor. One year later, intra-abdominal metastatic tumor was detected and resected. It had sarcomatoid features by light microscopy and failed to stain for epithelial markers by immunohistochemistry. DNA was extracted separately from the epithelial and sarcomatoid component of the primary tumor, intra-abdominal metastasis, and normal tissue. All exons of 230 cancer-associated genes were sequenced to an average read depth of >500-fold. This revealed multiple identical mutations in epithelial and sarcomatoid tumor compartments. Both compartments harbored 2 identical mutations, a truncating and a missense mutation, in the patched gene (PTCH1). This finding is not only of interest for a shared heritage of different subpopulations in a biphenotypic tumor, but also relevant clinically. It provides a rationale for the clinical use of hedgehog pathway inhibitors for treatment of patients affected by this tumor. Unfortunately, the patient reported herein died of metastatic disease before targeted therapy could be initiated.

BRAFV600Eis the most common mutation in cutaneous melanoma and has become the target of treatment for patients with metastatic melanoma. A number of methods are currently available to determine mutation status. Recently, a monoclonal antibody (VE1) against mutant BRAFV600Ewas generated. Its use permits assessment of the mutant protein expression throughout a tumor sample and may allow faster and cheaper determination of the mutation status in selected cases. However, for BRAFV600Eprotein expression analysis to be of clinical value, high sensitivity and specificity of the antibody is a prerequisite. In this study we analyzed 44 metastatic melanoma samples with a known BRAFV600Emutation status with immunohistochemical expression of the BRAFV600Eprotein. None of the 22 tumors that lacked the BRAFV600Emutation labeled with the antibody VE1. This set of VE1-immunonegative tumors included 4 metastatic lesions with the BRAFV600Kmutation. All 22 tumor samples that were known to carry the BRAFV600Emutation were immunoreactive with VE1. Sixteen of them stained strongly and homogenously throughout the tumor sample. However, 6 tumor samples contained both BRAFV600E-immunopositive and BRAFV600E-immunonegative cell populations. When the BRAF status was compared with immunoreactivity for melanocyte differentiation antigens, no significant difference in the expression of melan-A, microphthalmia transcription factor, gp100, or tyrosinase was found between mutant and wild-type tumors. In addition to metastatic lesions, we also examined 20 primary melanomas for the expression of BRAFV600E. Seven of 10 superficial spreading melanomas were immunoreactive with the antibody VE1. Five tumors were strongly and homogenously immunoreactive. In 2 primary tumors the staining was focal, involving only a subpopulation of the tumor. None of the nonsuperficial spreading melanomas was immunoreactive. In 7 primary tumors the mutation status could be analyzed: only tumors carrying the BRAFV600Emutation were immunoreactive with VE1. The high specificity and sensitivity of VE1 for the detection of mutant BRAFV600Esuggests a valuable reagent for clinical purposes. Heterogeneity in BRAF expression may be relevant for treatment response to BRAF inhibitors.

Recently a group of spitzoid melanocytic proliferations with loss of BAP1 expression has been reported. The lesions may occur sporadically or as part of a familial cancer syndrome. They have distinct histopathologic features characterized by a nevus-like silhouette and cytologic composition of large epithelioid melanocytes with oval vesicular nuclei, distinct nucleoli, and abundant cytoplasm with well-defined cytoplasmic borders. A characteristic immunohistochemical finding is loss of nuclear labeling for BAP1. In contrast to classic Spitz nevi, the lesions carry the BRAFV600Emutation. They may present as a pure large epithelioid cell proliferation or as a combined lesion in association with a conventional nevus. Here we report a series of 8 combined melanocytic lesions, in which a dominant large epithelioid cell proliferation with loss of BAP1 expression was associated and intimately admixed with a BAP1-positive conventional nevus. These biphenotypic lesions were from 6 patients, 3 female and 3 male, ranging in age from 16 to 59 years. Immunohistochemical analysis for BAP1 showed loss of nuclear labeling confined to the large epithelioid melanocyte subpopulation. The conventional melanocytes retained BAP1 expression. Both large epithelioid and conventional melanocytes were immunoreactive with the monoclonal antibody VE1, which recognizes the protein encoded by mutant BRAFV600E. In 6 cases the conventional nevus component was a compound nevus of small “type B” melanocytes. In 2 cases, the nevus remnant was entirely intradermal. The lesions described herein may represent a peculiar combined melanocytic nevus variant. However, longer follow-up and more studies are needed to determine the biological potential of the BAP1-negative melanocyte proliferations.

Melanoma may arise in association with andor simulate the appearance of a cellular blue nevus. The distinction of a cellular blue nevus with atypical features from blue nevus-like melanoma can be difficult. One rare setting, in which one may face this diagnostic challenge, is nodule formation in a large plaque-type blue nevus. We have previously reported 2 patients with cellular blue nevus-like subcutaneous nodules without overt malignant features and indolent clinical behavior. Herein we report a patient who developed malignant melanoma in association with a large plaque-type blue nevus. A 46-year-old woman with a history of “cellular blue nevus” of the breast that developed 7 years earlier during pregnancy had soft tissue nodules at the prior surgical site. She was found to have melanoma associated with a large plaque-type blue nevus, which involved the skin and subcutis of the chest wall and extended into breast parenchyma. Ten years after mastectomy and axillary node dissection with negative lymph nodes, the melanoma recurred as a subcutaneous chest wall nodule. Cytogenetic analysis revealed a number of aberrations, including deletion of 6q and gains of 6p and 8q. The patient then developed visceral metastases, first to the liver, and died of widely metastatic melanoma. In contrast, the cytogenetic findings of a previously reported cellular blue nevus-like nodule in a patient with a large plaque-type blue nevus were normal. That patient is still alive with no evidence of melanoma 16 years after the surgical excision of the subcutaneous cellular blue nevus-like nodule.