Reevaluation of established and new criteria in differential diagnosis of Spitz nevus and melanoma

High prevalence of p16 staining in malignant tumors

p16 (CDKN2A) is a member of the INK4 class of cell cycle inhibitors, which is often dysregulated in cancer. However, the prevalence of p16 expression in different cancer types is controversial. 15,783 samples from 124 different tumor types and 76 different normal tissue types were analyzed by immunohistochemistry in a tissue microarray format. p16 was detectable in 5,292 (45.0%) of 11,759 interpretable tumors. Except from adenohypophysis in islets of Langerhans, p16 staining was largely absent in normal tissues. In cancer, highest positivity rates were observed in uterine cervix squamous cell carcinomas (94.4%), non-invasive papillary urothelial carcinoma, pTaG2 (100%), Merkel cell carcinoma (97.7%), and small cell carcinomas of various sites of origin (54.5%-100%). All 124 tumor categories showed at least occasional p16 immunostaining. Comparison with clinico-pathological data in 128 vulvar, 149 endometrial, 295 serous ovarian, 396 pancreatic, 1365 colorectal, 284 gastric, and 1245 urinary bladder cancers, 910 breast carcinomas, 620 clear cell renal cell carcinomas, and 414 testicular germ cell tumors revealed only few statistically significant associations. Comparison of human papilloma virus (HPV) status and p16 in 497 squamous cell carcinomas of different organs revealed HPV in 80.4% of p16 positive and in 20.6% of p16 negative cancers (p<0.0001). It is concluded, that a positive and especially strong p16 immunostaining is a feature for malignancy which may be diagnostically useful in lipomatous, urothelial and possibly other tumors. The imperfect association between p16 immunostaining and HPV infection with high variability between different sites of origin challenges the use of p16 immunohistochemistry as a surrogate for HPV positivity, except in tumors of cervix uteri and the penis.

The Spectrum of Spitz Melanocytic Lesions: From Morphologic Diagnosis to Molecular Classification

Spitz tumors represent a distinct subtype of melanocytic lesions with characteristic histopathologic features, some of which are overlapping with melanoma. More common in the pediatric and younger population, they can be clinically suspected by recognizing specific patterns on dermatoscopic examination, and several subtypes have been described. We now classify these lesions into benign Spitz nevi, intermediate lesions identified as “atypical Spitz tumors” (or Spitz melanocytoma) and malignant Spitz melanoma. More recently a large body of work has uncovered the molecular underpinning of Spitz tumors, including mutations in the HRAS gene and several gene fusions involving several protein kinases. Here we present an overarching view of our current knowledge and understanding of Spitz tumors, detailing clinical, histopathological and molecular features characteristic of these lesions.

Risk factors in pediatric melanoma: a retrospective study of 39 cases

Pediatric melanoma is a rare form of the tumor whose epidemiology is widely increasing thanks to the improvement of dermoscopic and anatomopathologic diagnostic techniques. Although it is a tumor of considerable interest in adults, little has been described about the pediatric field. The objective of our study was then to identify the possible risk factors for the development of melanoma in the pediatric population. We performed a retrospective study conducted in the Melanoma and Skin Cancer Unit and Unit of Dermatology (Livorno, Italy). We analyzed a population of 38 children under 21 years with a diagnosis of melanoma. This population was compared with a control population of 114 children followed up in our dermatologic clinic. From our combined univariate-multivariate statistics analysis, the number of nevi [regression coefficient (RC) of 1.04 and odds ratio (OR) of 2.8 confidence interval (Cl, 1.2-6.6)], and family history of melanoma [RC of 1.99 and OR of 7.3 (Cl, 2.3-22.7)] emerged as possible risk factors for the development of melanoma. The identification of these elements would allow the physician to carry out a more targeted preliminary assessment of the patient, potentially decisive in cases of diagnostic doubt of the lesion. Our study also lays the foundations for identifying those children who, despite not having received a diagnosis of melanoma on histologic examination, should be considered as patients susceptible to a focused follow-up, because of the presence of the risk factors that emerged from our research.

Morphologic features in a series of 352 Spitz melanocytic proliferations help predict their oncogenic drivers

Spitz nevi are indolent melanocytic tumors arising preferentially during and after childhood. Over the last decades, recurrent oncogenic drivers, sparsely detected in melanoma, were identified in Spitz melanocytic proliferations. Therefore, the detection of such drivers appears as a relevant diagnostic tool to distinguish both entities. Interestingly, morphologic features might correlate with the oncogenic drivers. Thus, the goal of this study was to assess the performances of previously identified morphological criteria to predict the presence of specific drivers. In total, 352 Spitz melanocytic proliferations either with a genetically identified oncogenic driver or investigated for ALK, ROS1, and NTRK1 overexpression by immunohistochemistry were enrolled in the present study. The microscopic features of the cases were assessed blindly with regards to the molecular status and, performances of previously described morphological criteria to predict the molecular status were assessed applying the likelihood-ratio test (LHR). Overall, an oncogenic driver was identified in 76% of the cases (n = 268/352). No microscopic features allowed the reliable prediction of ROS1- and NTRK1-overexpressing cases. By contrast, a plexiform pattern can contribute to the recognition of ALK-overexpressing cases (LHR(+) = 6.14). Importantly, the pseudo-schwannoma variant was highly suggestive of NTRK3-rearranged cases (LHR(+) = 43). Moreover, atypical/malignant tumor (LHR(+) = 5.18), severe cellular atypia (LHR(+) = 5.07), and p16 loss (LHR(+) = 14) contribute to the recognition of MAP3K8-rearranged cases, while the presence of a sheet-like architecture (LHR(+) = 5.39) and a marked fibrosis of the stroma (LHR(+)=5.06) were predictive of BRAF-fused tumors. To conclude, our study confirms ALK-overexpressing, NTRK3-, MAP3K8-, and BRAF-rearranged cases harbored distinct morphologic features allowing their microscopic recognition.

Histopathologic and Molecular Diagnosis of Melanoma

Conventional histopathology is the primary means of melanoma diagnosis. Both architectural and cytologic features aid in discrimination of melanocytic nevi from melanoma. Communication between the clinician and pathologist regarding the history, examination, differential diagnosis, prior biopsy findings, method of sampling, and specimen orientation is critical to an accurate diagnosis. A melanoma pathology report includes multiple prognostic indicators to guide surgical and medical management. In challenging cases, immunohistochemistry and molecular diagnostics may be of benefit.

Imaging Mass Spectrometry-Based Proteomic Analysis to Differentiate Melanocytic Nevi and Malignant Melanoma

The discrimination of malignant melanoma from benign nevi may be difficult in some cases. For this reason, immunohistological and molecular techniques are included in the differential diagnostic toolbox for these lesions. These methods are time consuming when applied subsequently and, in some cases, no definitive diagnosis can be made. We studied both lesions by imaging mass spectrometry (IMS) in a large cohort (n = 203) to determine a different proteomic profile between cutaneous melanomas and melanocytic nevi. Sample preparation and instrument setting were tested to obtain optimal results in term of data quality and reproducibility. A proteomic signature was found by linear discriminant analysis to discern malignant melanoma from benign nevus (n = 113) with an overall accuracy of >98%. The prediction model was tested in an independent set (n = 90) reaching an overall accuracy of 93% in classifying melanoma from nevi. Statistical analysis of the IMS data revealed mass-to-charge ratio (m/z) peaks which varied significantly (Area under the receiver operating characteristic curve > 0.7) between the two tissue types. To our knowledge, this is the largest IMS study of cutaneous melanoma and nevi performed up to now. Our findings clearly show that discrimination of melanocytic nevi from melanoma is possible by IMS.

Mimics of melanoma in reflectance confocal microscopy

The diagnosis of melanoma is challenging for both dermatologists and oncologists. Incidence of melanoma increases at a rate of 3-7% per year. Usage of modern tools such as dermoscopy and in vivo reflectance confocal microscopy improve early diagnosis and can save a life. There are a few melanoma simulators which can cause confusion and mislead in the differential diagnosis. This study aims to present skin lesions which can be similar to melanoma in confocal microscopy and to emphasize the importance of a detailed differential diagnosis. We describe five melanocytic lesions similar to melanoma and misleading confocal features. Although in vivo reflectance confocal microscopy is very useful in differentiating melanocytic lesions, histopathology evaluation in cases of melanoma mimics is definitive.

ALK-positive compound Spitz nevus with extensive perineural and intraneural neurotropism

Historically recognized by their characteristic histopathologic features, Spitz neoplasms are now known to be molecularly defined by mutually exclusive recurrent abnormalities that cause activation of the MAPK pathway. Spitz neoplasms with ALK rearrangements frequently demonstrate polypoid growth with a plexiform arrangement of nested, fusiform melanocytes in intersecting fascicles. Although neurotropism has been described in indolent Spitz neoplasms, this feature is not frequently mentioned in publications on histopathologic assessment of this group of melanocytic tumors. Here, we present an unusual case of a 3-year-old female with an ALK-positive compound Spitz nevus with extensive perineural and intraneural neurotropism occurring on the vermilion border of the lower lip.

A Rare Case of Solitary Pituitary Metastasis From Spitzoid Melanoma Detected by FDG PET/CT

A 33-year-old man had a diagnosis of a spitzoid melanoma by dorsal skin biopsy. During the oncological follow-up, patient underwent whole-body FDG PET/CT for restaging purpose. FDG PET/CT showed a large necrotic mass of the pituitary gland, subsequently confirming a solitary pituitary metastasis from spitzoid melanoma.

The 2018 World Health Organization Classification of Cutaneous, Mucosal, and Uveal Melanoma: Detailed Analysis of 9 Distinct Subtypes Defined by Their Evolutionary Pathway

CONTEXT.—

There have been major advances in the understanding of melanoma since the last revision of the World Health Organization (WHO) classification in 2006.

OBJECTIVE.—

To discuss development of the 9 distinct types of melanoma and distinguishing them by their epidemiology, clinical and histologic morphology, and genomic characteristics. Each melanoma subtype is placed at the end of an evolutionary pathway that is rooted in its respective precursor, wherever appropriate and feasible, based on currently known data. Each precursor has a variable risk of progression culminating in its fully evolved, invasive melanoma.

DATA SOURCES.—

This review is based on the "Melanocytic Tumours" section of the 4th edition of the WHO Classification of Skin Tumours, published in 2018.

CONCLUSIONS.—

Melanomas were divided into those etiologically related to sun exposure and those that are not, as determined by their mutational signatures, anatomic site, and epidemiology. Melanomas on the sun-exposed skin were further divided by the histopathologic degree of cumulative solar damage (CSD) of the surrounding skin, into low and high CSD, on the basis of degree of associated solar elastosis. Low-CSD melanomas include superficial spreading melanomas and high-CSD melanomas incorporate lentigo maligna and desmoplastic melanomas. The "nonsolar" category includes acral melanomas, some melanomas in congenital nevi, melanomas in blue nevi, Spitz melanomas, mucosal melanomas, and uveal melanomas. The general term melanocytoma is proposed to encompass "intermediate" tumors that have an increased (though still low) probability of disease progression to melanoma.

Genomic Landscape of Spitzoid Neoplasms Impacting Patient Management

Spitzoid neoplasms are a distinct group of melanocytic proliferations characterized by epithelioid and/ or spindle shaped melanocytes. Intermediate forms that share features of both benign Spitz nevi (SN) and Spitz melanoma, i.e., malignant Spitz tumor (MST) represent a diagnostically and clinically challenging group of melanocytic lesions. A multitude of descriptive diagnostic terms exist for these ambiguous lesions with atypical Spitz tumor (AST) or Spitz tumor of uncertain malignant potential (STUMP) just naming two of them. This diagnostic gray zone creates confusion and high insecurity in clinicians and in patients. Biological behavior and clinical course of this intermediate group still remains largely unknown, often leading to difficulties with uncertainties in clinical management and prognosis. Consequently, a better stratification of Spitzoid neoplasms in benign and malignant forms is required thereby keeping the diagnostic group of AST/STUMP as small as possible. Ancillary diagnostic techniques such as immunohistochemistry, comparative genomic hybridization, fluorescence in situ hybridization, next generation sequencing, micro RNA and mRNA analysis as well as mass spectrometry imaging offer new opportunities for the distinct diagnosis, thereby allowing the best clinical management of Spitzoid neoplasms. This review gives an overview on these additional diagnostic techniques and the recent developments in the field of molecular genetic alterations in Spitzoid neoplasms. We also discuss how the recent findings might facilitate the diagnosis and stratification of atypical Spitzoid neoplasms and how these findings will impact the diagnostic work up as well as patient management. We suggest a stepwise implementation of ancillary diagnostic techniques thereby integrating immunohistochemistry and molecular pathology findings in the diagnosis of challenging ambiguous Spitzoid neoplasms. Finally, we will give an outlook on pending future research objectives in the field of Spitzoid melanocytic lesions.

[Dermatoscopic-pathological correlation of melanocytic skin lesions]

There is no doubt that dermatopathology is the most important method to decide if a melanocytic lesion is benign or malignant; however, like most morphologic examinations, dermatopathology is subjective. A recent study demonstrated that the pathologic diagnosis of melanocytic skin lesions has a high variability. Reports with false-positive or false-negative diagnoses are relatively common. The pathologic examination of melanocytic lesions also has observer-independent limitations and one has to accept that some melanocytic lesions cannot be classified as benign or malignant with confidence by dermatopathology alone. If a confident diagnosis is not possible a dermatoscopic-pathologic correlation may be helpful. This, however, is only possible if dermatoscopic images are available and if the dermatopathologist knows how to interpret dermatoscopic structures. A dermatoscopic-pathologic correlation is not useful in all difficult melanocytic lesions but it should be considered in difficult flat pigmented lesions. In these cases dermatoscopy may provide even more important additional information than molecular findings.