Amplification of mutant NRAS in melanocytic tumors with features of Spitz tumors

NRAS activating mutations are prevalent in melanocytic neoplasia, occurring in a subset of common acquired melanocytic nevi and approximately 30% of cutaneous melanomas. In this study, we describe a cohort of seven distinctive melanocytic tumors characterized by activating point mutations in codon 61 of NRAS with amplification of the mutant NRAS allele and shared clinicopathologic features. These tumors occurred predominantly in younger patients, with a median age of 20 years (ranging from 6 to 56). They presented as papules on the helix of the ear (four cases) or extremities (three cases). Microscopically, the tumors were cellular, relatively well-circumscribed, compound or intradermal proliferations. The tumor cells often extended into the deep reticular dermis, and involved the superficial subcutaneous fat in some cases. The melanocytes were epithelioid to spindled with moderate amounts of cytoplasm and conspicuous nucleoli. They were arranged in short plexiform fascicles, nests, and cords. Some cases had occasional pleomorphic and multinucleated melanocytes. Rare dermal mitotic figures were present in all cases. The dermis contained thick collagen bundles and minimal solar elastosis. Follow-up data were available for five patients, with a median period of 4.2 years (ranging from 1 to 9 years), during which no recurrences or metastases were reported. Our series highlights a clinicopathologically and molecularly distinctive subset of NRAS-mutated tumors with amplification of the mutant NRAS allele.

Diagnostic Algorithm to Subclassify Atypical Spitzoid Tumors in Low and High Risk According to Their Methylation Status

Current diagnostic algorithms are insufficient for the optimal clinical and therapeutic management of cutaneous spitzoid tumors, particularly atypical spitzoid tumors (AST). Therefore, it is crucial to identify new markers that allow for reliable and reproducible diagnostic assessment and can also be used as a predictive tool to anticipate the individual malignant potential of each patient, leading to tailored individual therapy. Using Reduced Representation Bisulfite Sequencing (RRBS), we studied genome-wide methylation profiles of a series of Spitz nevi (SN), spitzoid melanoma (SM), and AST. We established a diagnostic algorithm based on the methylation status of seven cg sites located in TETK4P2 (Tektin 4 Pseudogene 2), MYO1D (Myosin ID), and PMF1-BGLAP (PMF1-BGLAP Readthrough), which allows the distinction between SN and SM but is also capable of subclassifying AST according to their similarity to the methylation levels of Spitz nevi or spitzoid melanoma. Thus, our epigenetic algorithm can predict the risk level of AST and predict its potential clinical outcomes.

A reappraisal of the epidemiology of Spitz neoplasms in the molecular era: A retrospective cohort study

BACKGROUND

Previous studies suggest that Spitz neoplasms occur primarily in younger patients, leading pathologists to shy away from diagnosing a benign Spitz neoplasm in the elderly. With the advent of genomic sequencing, there is a need for reappraisal of the epidemiology of Spitz neoplasms in the modern molecular era.

OBJECTIVE

We aim to reassess the epidemiology of Spitz neoplasms incorporating next-generation sequencing.

METHODS

We looked at 53,814 non-Spitz neoplasms and 1260 Spitz neoplasms including 286 Spitz neoplasms with next-generation sequencing testing and collected various epidemiologic data.

RESULTS

In our general pool of cases, the proportion of Spitz neoplasm cases occurring is relatively the same in each of the first 4 decades of life with a precipitous drop in the fifth decade. In assessing a group of genomically verified cases of Spitz neoplasms, the drop was much less significant and up to 20% of all Spitz neoplasm cases occurred in patients over 50 years of age.

LIMITATIONS

Limitations included the number of genetically verified Spitz neoplasm cases available and a possible bias as to which cases undergo genomic testing.

CONCLUSION

Genomic verification may allow more confident diagnosis of Spitz neoplasms in patients over 50 years of age and avoid melanoma overdiagnosis.

PRAME immunohistochemistry compared to traditional FISH testing in spitzoid neoplasms and other difficult to diagnose melanocytic neoplasms

PRAME (PReferentially expressed Antigen in Melanoma) is a gene first identified in melanoma. It has been proposed as a useful marker to differentiate melanoma from benign melanocytic neoplasms. Recently genomic testing using fluorescence in situ hybridization has been used to aid in the diagnosis of difficult melanocytic neoplasms. We have compared PRAME staining to FISH testing results in 83 difficult to classify melanocytic neoplasms which showed spitzoid histologic features. A relatively low sensitivity of 29.6% and high specificity of 76.8% is seen with PRAME staining as compared to genomic testing with fluorescence in situ hybridization. This study highlights the limitations of PRAME staining in spitzoid neoplasms.

Concordance of reflectance confocal microscopy and gene expression profiling for melanocytic lesions with uncertain malignant potential: A case series

For a small yet significant proportion of melanocytic lesions, histopathologic analysis may be unable to definitively evaluate malignant potential. These cases may signify a specific need for newer ancillary diagnostic technologies, including in vivo reflectance confocal microscopy (RCM) and gene expression profiling (GEP), both of which are highly sensitive in the diagnosis of melanoma. We report four cases of clinically suspicious melanocytic lesions that lacked definitive malignant features on histopathology and that were aided by use of RCM and GEP. Three of the four cases showed concordance between RCM and GEP in the diagnosis of melanoma. In one case, RCM was suggestive of melanoma; on the other hand, GEP and histopathology supported a final diagnosis of compound Spitz nevus. These cases support the role of RCM as a novel, non-invasive diagnostic tool to aid in the diagnosis of clinically suspicious melanocytic lesions with uncertain malignant potential, although RCM may have relatively lower accuracy for some atypical spitzoid lesions.

Combined utility of p16 and BRAF V600E in the evaluation of spitzoid tumors: Superiority to PRAME and correlation with FISH

BACKGROUND

Spitzoid melanocytic neoplasms are diagnostically challenging; criteria for malignancy continue to evolve. The ability to predict chromosomal abnormalities with immunohistochemistry (IHC) could help select cases requiring chromosomal evaluation.

METHODS

Fluorescence in situ hybridization (FISH)-tested spitzoid neoplasms at our institution (2013-2021) were reviewed. p16, BRAF V600E, and preferentially expressed antigen in melanoma (PRAME) IHC results were correlated with FISH.

RESULTS

A total of 174 cases (1.9F:1M, median age 28 years; range, 5 months-74 years) were included; final diagnoses: Spitz nevus (11%), atypical Spitz tumor (47%), spitzoid dysplastic nevus (9%), and spitzoid melanoma (32%). Sixty (34%) were FISH positive, most commonly with absolute 6p25 gain (RREB1 > 2). Dermal mitotic count was the only clinicopathologic predictor of FISH. Among IHC-stained cases, p16 was lost in 55 of 134 cases (41%); loss correlated with FISH positive (p < 0.001, Fisher exact test). BRAF V600E (14/88, 16%) and PRAME (15/56, 27%) expression did not correlate with FISH alone (p = 0.242 and p = 0.359, respectively, Fisher exact test). When examined together, however, p16-retained/BRAF V600E-negative lesions had low FISH-positive rates (5/37, 14%; 4/37, 11% not counting isolated MYB loss); all other marker combinations had high rates (56%-75% of cases; p < 0.001).

CONCLUSIONS

p16/BRAF V600E IHC predicts FISH results. "Low-risk" lesions (p16⁺ /BRAF V600E^- ) uncommonly have meaningful FISH abnormalities (11%). PRAME may have limited utility in this setting.

Next-generation sequencing improves agreement and accuracy in the diagnosis of Spitz and spitzoid melanocytic lesions

BACKGROUND

Spitzoid melanocytic neoplasms can be challenging to diagnose on histopathology alone. Next-generation sequencing (NGS) offers promise as a valuable aid in the diagnosis. Recently, one study reported increased inter-rater agreement in the diagnosis of spitzoid melanocytic neoplasms among 20 expert melanoma pathologists after incorporating NGS data. We hypothesized that NGS would carry a similar utility in a broader group of dermatopathologists and general pathologists.

METHODS

Sixty-three participants of a live online (www.Dermpedia.org) CME course rendered a diagnosis on 70 cases composed of melanocytic neoplasms with spitzoid features. In Survey 1, cases included H&E slides and demographic information only, while Survey 2 included NGS data.

RESULTS

With NGS information, inter-rater agreement significantly improved from "fair" to "almost perfect" and from "fair" to "substantial" for categorizing lesions as Spitz versus non-Spitz and conventional melanoma versus not, respectively. There was also an increase in diagnostic accuracy, evidenced by improved recognition of three metastatic tumors as being conventional melanomas.

CONCLUSION

The study supports the adoption of NGS as a valuable diagnostic adjunct for both expert and broader dermatopathologists in their assessments of spitzoid neoplasms.

Risk factors for the development of Spitz neoplasms

BACKGROUND/OBJECTIVES

The principal environmental risk factor for conventional nevi and melanomas is ultraviolet exposure. However, little is known about genetic or environmental risk factors for developing Spitz tumors. This study investigates risk factors associated with Spitz neoplasms.

METHODS

Patients with Spitz tumors seen at Northwestern Memorial Hospital and Lurie Children's Hospital were surveyed with a 16-item questionnaire about environmental and inherited factors. Spitz tumor patients were compared to a pediatric control cohort from a similar clinical setting. This was supplemented with a meta-analysis of genetic and environmental causes of Spitz neoplasms.

RESULTS

One hundred and six Spitz and 58 control surveys were obtained and no statistically significant differences in genetic or environmental risk factors were found between Spitz and control groups.

CONCLUSION

Our data and meta-analysis suggest that typical risk factors associated with melanoma are not significantly associated with Spitz tumors. Identification of relevant genetic or environmental risk factors will likely require larger and population-based studies.

Spitz nevus with EHBP1-ALK fusion and distinctive membranous localization of ALK

ALK rearrangements define a histopathologically distinctive but diverse subset of Spitz tumors characterized by fusiform to epithelioid melanocytes with frequent fascicular growth and ALK overexpression. Molecularly, these tumors are characterized by fusions between ALK and a variety of other genes, most commonly TPM3 and DCTN1. We describe an unusual case of a Spitz nevus occurring in a 13-year-old female that manifested ALK immunopositivity with cell membrane localization. The proliferation was polypoid and composed of elongated nests of epithelioid melanocytes with enlarged nuclei, prominent nucleoli, and abundant cytoplasm without significant atypia and lacking mitotic figures. The nevus exhibited strong and diffuse expression of p16. Targeted next-generation RNA sequencing revealed an in-frame EHBP1-ALK fusion, which has been reported only once in the literature. EHBP1 encodes an adaptor protein with plasma membrane targeting potential. Together, these findings suggest that the 5' ALK fusion partner in Spitz tumors may dictate the subcellular localization of the ALK chimeric oncoprotein. In summary, this case highlights a rare ALK fusion associated with a distinct immunohistochemical staining pattern and further expands the spectrum of ALK-rearranged melanocytic tumors. This article is protected by copyright. All rights reserved.

Preferentially expressed antigen in melanoma and p16 expression in acral melanocytic neoplasms

Acral melanocytic neoplasms often pose diagnostic difficulty. Preferentially expressed antigen in melanoma (PRAME) expression and loss of p16 expression have diagnostic utility in melanocytic tumors. We examined PRAME and p16 expression in 30 acral melanocytic neoplasms (n = 11 nevi; n = 2 dysplastic nevi; n = 7 Spitz nevi; n = 10 acral melanomas). PRAME was scored as % positive nuclei: negative = 0%; 1% to 25% = 1+; 25% to 50% = 2+; 50% to 75% = 3+, or positive: 75% to 100% = 4+. p16 expression was defined as retained (homogeneous or checkerboard) or lost (complete or partial/regionally). PRAME expression was negative in all benign, dysplastic, and Spitz nevi. Conversely, all acral melanomas were diffusely (4+) positive for PRAME expression. p16 expression was retained in all benign acral nevi (8/11 homogeneous, 3/11 checkerboard), completely lost in one dysplastic nevus, and retained in all acral Spitz nevi (3/7 homogeneous, 4/7 checkerboard). p16 was retained in five of 10 acral melanomas (3/10 homogeneous; 2/10 checkerboard), and negative in five of 10 acral melanomas (absent in 3/10, partially lost in 2/10). Our data suggest that 4+ PRAME expression is highly sensitive and specific in the setting of acral melanomas and is a more predictive diagnostic tool compared with p16 immunohistochemistry.

Cross-reactivity of NRASQ61R antibody in a subset of Spitz nevi with 11p gain: a potential confounding factor in the era of pathway-based diagnostic approach

The most recent World Health Organization classification for skin tumors (2018) categorizes melanomas and their precursor lesions, benign or intermediate, into nine pathways based not only on their clinical and histomorphologic characteristics but also on their molecular profile and genetic fingerprint. In an index case of a partially sampled atypical spitzoid lesion, which proved to be an 11p-amplified Spitz nevus with HRASQ61R mutation, we observed cross-reactivity with the NRASQ61R antibody (clone SP174). Overall, we assessed the status of HRAS and NRAS genes and their immunoreaction to NRASQ61R antibody in 16 cases of 11p-amplified Spitz nevi/atypical Spitz tumors. We also assessed the immunoexpression of NRASQ61R antibody in various malignancies with proven BRAFV600E, NRASQ61R, L or K, KRASQ61R and HRASQ61R, and HRASQ61R mutations and ALK+ Spitz lesions. Finally, we assessed the expression of PReferentially expressed Antigen in MElanoma (PRAME) immunohistochemistry in our 11p Spitz cohort. Three of 16 cases (3/16) harbored the HRASQ61R mutation and exhibited diffuse immunoreaction with the NRASQ61R antibody. All the cases in our cohort were negative for the NRASQ61R mutation. All NRASQ61R-, KRASQ61R-, and HRASQ61R-mutated neoplasms were positive for the antibody, further supporting the cross-reactivity between the RAS proteins. All the cases of our cohort were essentially negative for PRAME immunohistochemistry. In the era of pathway-based approach in the diagnosis of melanocytic neoplasms, the cross-reactivity between the NRASQ61R- and HRASQ61R-mutated proteins can lead to a diagnostic pitfall in the assessment of lesions with spitzoid characteristics.

Spitz nevi in African Americans: A retrospective chart review of 11 patients

BACKGROUND

Spitz nevi are benign melanocytic neoplasms that typically present as rapidly growing solitary lesions on the head, neck, or lower extremities. Very rare reports have been described in African Americans.

METHODS

A single-institution 29-year retrospective review of African American patients diagnosed with Spitz nevi was thoroughly analyzed in order to characterize these rare clinical and histopathologic presentations.

RESULTS

Eleven African Americans with spitzoid lesions were identified. Seven (64%) cases were in pediatric patients and nine (82%) were in females. Most lesions were hyperpigmented (73%) and elevated (82%). Six (55%) were compound Spitz nevi, three (27%) were dermal Spitz nevi, and two (18%) were junctional Spitz nevi. Two lesions had more than one atypical feature. Histopathologically, common features were symmetry, sharp circumscription, pagetoid spread (55%) with most being centrally, predominance of epithelioid cells (64%), Kamino bodies (45%), slight pigmentation (46%), maturation of dermal component with depth, and lack of subcutaneous fat involvement or ulceration. Excision was performed on all patients and there were no recurrences although follow-up was limited.

CONCLUSION

Awareness of the possibility and various presentations of Spitz nevi in African Americans will help prevent misdiagnosis.

Targeted next generation sequencing (NGS) to classify melanocytic neoplasms

This study piloted a pan-solid-tumor next generation sequence (NGS)-based laboratory developed test as a diagnostic aid in melanocytic tumors. 31 cases (4 "epithelioid" nevi, 5 blue nevi variants, 7 Spitz tumors [3 benign and 4 malignant] and 15 melanomas) were evaluated. All tumors [median diameter 7 mm (range 4-15 mm); median thickness 2.25 mm (range 0.25-12 mm)] yielded satisfactory results. The number of small nucleotide variants/tumor was significantly different between melanoma (median 18/tumor, range 4-71) and all other lesions (median 8/tumor, range 3-17) (P < 0.004) and malignant (median 16/tumor, range 4-71) vs benign lesions (median 7/tumor, range 3-14) (P = 0.01). BRAF, MET, NTRK1, and ROS fusions only occurred in benign Spitz tumors; EML4 fusion, BRAF, MAP2K1 and TERT mutations occurred in malignant Spitz tumors and/or melanoma. Amplifications and NRAS and NF1 mutations only occurred in melanoma. Most melanomas contained >1 pathogenic alteration. Developed NGS-based criteria correctly classified all malignant lesions in this series. 10/12 cases showed concordance with FISH; consensus diagnosis agreed with NGS classification in FISH-non-concordant cases. This pilot study suggests that NGS may be an effective diagnostic adjunct comparable to FISH, but further studies with larger numbers of cases are needed.

A case of molecularly confirmed BAP1 inactivated melanocytic tumor with retention of immunohistochemical expression: A confounding factor

BRCA1-associated Protein 1 (BAP1)-inactivated melanocytic nevi/tumors (BIMT) have distinct morphologic features. A typical case exhibits a biphasic population of cytologically bland conventional melanocytes and a second proliferation of larger epithelioid melanocytes with abundant eosinophilic cytoplasm. The vast majority of cases harbor BRAF V600E in both components with bi-allelic inactivation of BAP1 in the epithelioid component by various molecular mechanisms resulting in loss of nuclear protein expression, which can be demonstrated by immunohistochemistry. We present a case of BIMT with histopathologic features highly suggestive of this entity but unexpected retention of nuclear expression of the BAP1 protein. Subsequent molecular tests showed heterozygous loss of the BAP1 locus on the short arm of chromosome 3 (3p21.1) by chromosomal microarray analysis (CMA) and a suspected c.505C>T p.H169Y pathogenic variant identified by DNA sequencing that was subsequently confirmed by primer-specific SNaPshot mini-sequencing. In light of the heterozygous deletion of BAP1, this variant in the remaining allele encodes a catalytically inactive BAP1 mutant protein as shown in functional studies. The presence of a nonfunctional allele within the nucleus combined with a heterozygous deletion of BAP1 explains the clear and characteristic BIMT morphology observed by histopathology. This case underlines the potential importance of molecular diagnostics when protein expression studies do not correlate with morphology.

Histologic features of melanoma associated with germline mutations of CDKN2A, CDK4, and POT1 in melanoma-prone families from the United States, Italy, and Spain

BACKGROUND

CDKN2A, CDK4, and POT1 are well-established melanoma-susceptibility genes.

OBJECTIVE

We evaluated melanoma histopathology for individuals with germline mutations of CDKN2A, CDK4, and POT1.

METHODS

We assessed histopathology for melanomas diagnosed in melanoma-prone families (≥2 individuals with melanoma) from the United States, Italy, and Spain. Comparisons between mutation carriers and noncarriers (no mutation) were adjusted for age, sex, Breslow depth, and correlations among individuals within the same family.

RESULTS

Histologic slides were evaluated for 290 melanomas (139 from 132 noncarriers, 122 from 68 CDKN2A carriers, 10 from 6 CDK4 carriers, and 19 from 16 POT1 carriers). Superficial spreading was the predominant subtype for all groups. Spitzoid morphology (>25% of tumor) was observed in 10 of 15 invasive melanomas (67%) from POT1 carriers (P < .0001 vs noncarriers). This finding was independently confirmed by 3 expert melanoma dermatopathologists in 9 of 15 invasive melanomas (60%). In situ and invasive melanomas from CDKN2A and CDK4 carriers were histologically similar to melanomas from noncarriers.

LIMITATIONS

Limited sample sizes for rare melanoma-susceptibility syndromes (CDK4, POT1).

CONCLUSION

Spitzoid morphology was associated with POT1 mutations suggesting that telomere dysfunction (POT1 mutations) may contribute to spitzoid differentiation in melanocytic tumors.

BRCA1-associated protein (BAP1)-inactivated melanocytic tumors

Although discussed using variable terminology, cutaneous BRCA1-associated protein (BAP1)-inactivated melanocytic tumor (BIMT) has been considered a discrete diagnostic entity since 2011. Here, we review the initial genomic studies that identified these distinct melanocytic tumors and the clinical and histopathological features that define these tumors. These epithelioid, predominantly dermal, and melanocytic tumors present as erythematous nodules and histopathologically have features that may overlap with Spitz nevi and nevoid melanoma. There is no sex predilection, and cutaneous BIMTs can appear at any age; however, in most familial (germline mutant) cases patients have multiple cutaneous tumors with a first diagnosis in the second or third decade of life; ocular melanoma and other tumors are increasingly identified in these kindreds with germline BAP1 mutation. These tumors have been described with a myriad of terms including: Wiesner nevus, nevoid melanoma-like melanocytic proliferation (NEMMP), BAP1 mutant Spitz nevus, BAP1 mutant nevoid melanoma, cutaneous BAPoma, and most recently cutaneous BIMT.

Clinical and dermoscopic characterization of pediatric and adolescent melanomas: Multicenter study of 52 cases

BACKGROUND

Knowledge regarding the morphologic spectrum of pediatric melanoma (PM) is sparse, and this may in part contribute to delay in detection and thicker tumors.

OBJECTIVE

To analyze the clinicodermoscopic characteristics of PM.

METHODS

Retrospective study of 52 melanomas diagnosed in patients before the age of 20 years.

RESULTS

On the basis of its clinical, dermoscopic, and histopathologic characteristics, PM can be classified as spitzoid or nonspitzoid. The nonspitzoid melanomas (n = 37 [72.3%]) presented in patients with a mean age of 16.3 years (range, 8-20) and were associated with a high-risk phenotype and a pre-existing nevus (62.2%). The spitzoid melanomas (n = 15 [27.7%]) were diagnosed in patients at a mean age of 12.5 years (range, 2-19) and were mostly de novo lesions (73.3%) located on the limbs (73.3%). Whereas less than 25% of PMs fulfilled the modified clinical ABCD criteria (amelanotic, bleeding bump, color uniformity, de novo at any diameter), 40% of spitzoid melanomas did. Dermoscopic melanoma criteria were found in all cases. Nonspitzoid melanomas tended to be multicomponent (58.3%) or have nevus-like (25%) dermoscopic patterns. Spitzoid melanomas revealed atypical vascular patterns with shiny white lines (46.2%) or an atypical pigmented spitzoid pattern (30.8%). There was good correlation between spitzoid subtype histopathologically and dermoscopically (κ = 0.66).

LIMITATIONS

A retrospective study without re-review of pathologic findings.

CONCLUSION

Dermoscopy in addition to conventional and modified clinical ABCD criteria helps in detecting PM. Dermoscopy assists in differentiating spitzoid from nonspitzoid melanomas.

The utilization of spitz-related nomenclature in the histological interpretation of cutaneous melanocytic lesions by practicing pathologists: results from the M-Path study

BACKGROUND

Spitz nevi, atypical Spitz tumors and spitzoid melanomas ('spitzoid lesions') represent controversial and poorly understood cutaneous melanocytic lesions that are difficult to diagnose histologically. It is unknown how these terms are used by pathologists.

METHODS

We describe use of Spitz-related terminology using data from the Melanoma Pathology (M-Path) study database comprising pathologists' interpretations of biopsy slides, a nation-wide study evaluating practicing US pathologists' (N = 187) diagnoses of melanocytic lesions (8976 independent diagnostic assessments on 240 total test cases, with 1 slide per case).

RESULTS

Most pathologists (90%) used the Spitz-related terminology. However, significant variation exists in which specific lesions were diagnosed as spitzoid and in the corresponding treatment recommendations. Recommendations ranged from 'no further treatment' to 'wide excision of 10 mm or greater' with no category capturing more than 50% of responses. For spitzoid melanoma diagnoses, 90% of pathologists recommended excision with ≥10 mm margin. Pathologists report less confidence in diagnosing these lesions compared with other melanocytic proliferations and are more likely to request second opinions and additional clinical information (all p < 0.05).

CONCLUSIONS

Spitzoid lesions are often not classified in any standardized way, evoke uncertainty in diagnosis by pathologists, and elicit variability in treatment recommendations.

Developmental roles of Rhomboid proteases

Rhomboid proteins have emerged as one of the most tantalizing and diverse families of proteases. Gene duplication events and structural alterations have sculpted the varied roles of this protein family, maintaining a conserved structural core throughout the bacterial, plant and animal kingdoms. Unresolved questions pop up at many junctions. This review will focus on a distinct class of Rhomboid proteins that plays an essential role in development. It will outline the diverse mechanisms by which these proteins are regulated, and the implications on the biological processes they control. While most of the review will deal with Rhomboids in Drosophila, a system that has been studied in the greatest detail, it will also explore parallels and differences in the function of Rhomboids in the flour beetle T. casteneum and the worm C. elegans.

Global microRNA profiling for diagnostic appraisal of melanocytic Spitz tumors

BACKGROUND

Melanoma skin cancer remains the leading cause of skin cancer-related deaths. Spitz lesions represent a subset of melanocytic skin lesions characterized by epithelioid or spindled melanocytes organized in nests. These lesions occupy a spectrum ranging from benign Spitz and atypical Spitz lesions all the way to malignant Spitz tumors. Appropriate management is reliant on accurate diagnostic classification, yet this effort remains challenging using current light microscopic techniques. The discovery of novel biomarkers such as microRNAs (miR) may ultimately be a useful diagnostic adjunct for the evaluation of Spitz lesions. miR expression profiles have been suggested for non-Spitz melanomas but have yet to be ascribed to Spitz lesions. We hypothesized that distinct miR expression profiles would be associated with different lesions along the Spitz spectrum.

MATERIALS AND METHODS

RNAs extracted from paraffin-embedded, formalin-fixed tissues of 11 resected skin lesions including benign nevi (n = 2), benign Spitz lesions (n = 3), atypical Spitz lesions (n = 3), and malignant Spitz tumors (n = 3) were analyzed by the NanoString platform for simultaneous evaluation of over 800 miRs in each patient sample.

RESULTS

Benign Spitz lesions had increased expression of miR-21-5p and miR-363-3p compared with those of benign nevi. Malignant Spitz lesions exhibited overexpression of miR-21-5p, miR-155-5p, and miR-1283 relative to both benign nevi and benign Spitz tumors. Notably, atypical Spitz tumors had increased expression of miR-451a and decreased expression of miR-155-5p expression relative to malignant Spitz lesions. Conversely, atypical Spitz lesions had increased expression of miR-21-5p, miR-34a-5p, miR-451a, miR-1283, and miR-1260a relative to benign Spitz tumors.

CONCLUSIONS

Overall, distinct miR profiles are suggested among Spitz lesions of varying malignant potential with some similarities to non-Spitz melanoma tumors. This work demonstrates the feasibility of this analytic method and forms the basis for further validation studies.

A feedback amplification loop between stem cells and their progeny promotes tissue regeneration and tumorigenesis

Homeostatic renewal of many adult tissues requires balanced self-renewal and differentiation of local stem cells, but the underlying mechanisms are poorly understood. Here we identified a novel feedback mechanism in controlling intestinal regeneration and tumorigenesis in Drosophila. Sox21a, a group B Sox protein, is preferentially expressed in the committed progenitor named enteroblast (EB) to promote enterocyte differentiation. In Sox21a mutants, EBs do not divide, but cannot differentiate properly and have increased expression of mitogens, which then act as paracrine signals to promote intestinal stem cell (ISC) proliferation. This leads to a feedback amplification loop for rapid production of differentiation-defective EBs and tumorigenesis. Notably, in normal intestine following damage, Sox21a is temporally downregulated in EBs to allow the activation of the ISC-EB amplification loop for epithelial repair. We propose that executing a feedback amplification loop between stem cells and their progeny could be a common mechanism underlying tissue regeneration and tumorigenesis.

DOI:http://dx.doi.org/10.7554/eLife.14330.001

Within our bodies we have stem cells that are responsible for maintaining many of our tissues in a healthy state and healing wounds after an injury. When these adult stem cells divide, they can produce daughter cells. Through a process called differentiation, these daughter cells can become mature cells that replace old or damaged cells. However, the stem cells also produce copies of themselves – in a process known as self-renewal – to ensure that an organ does not run out of stem cells. The rates of differentiation and self-renewal must be carefully balanced: too much differentiation can eventually lead to the degeneration of the tissue, whereas too much self-renewal can cause tumors to develop.

One of the main questions in the stem cell field is how tissues and organs balance these opposing processes. The fruit fly mid-gut is a model system for investigating this question, and is similar to the intestine of mammals. The mid-gut is composed of three main cell types: intestinal stem cells, enteroblasts (immediate daughter cells of the stem cells) and enterocytes (fully differentiated, mature cells).

Previously published data showed that a protein called Sox21a is present in the intestinal stem cells and enteroblasts, but not in the mature enterocytes. To investigate the role of Sox21a in more detail, Chen et al. deleted the gene that produces Sox21a in fruit flies. These mutant flies developed tumors in their guts, indicating that Sox21a is a tumor suppressor. Further experiments revealed that Sox21a normally drives enteroblasts to differentiate into enterocytes, and also prevents the enteroblasts from communicating with the stem cells to indicate that more enteroblasts are needed.

In further experiments, Chen et al. gave otherwise healthy fruit flies a drug that injured their guts. This caused Sox21a activity to decrease temporarily, allowing more enteroblasts to be produced from intestinal stem cells to repair the damage. The mid-gut therefore has an intricate “feedback amplification” system that maintains an appropriate number of each type of cell.

In future, other experiments will be needed to determine whether similar feedback amplification systems are found in other tissues, and to investigate the extent to which these systems are found in mammals. Furthermore, understanding this process in more depth could increase our knowledge about how cancerous tumors grow.

DOI:http://dx.doi.org/10.7554/eLife.14330.002

Spen is required for pigment cell survival during pupal development in Drosophila

Apoptosis is required during development to eliminate superfluous cells and sculpt tissues; spatial and timed control of apoptosis ensures that the necessary number of cells is eliminated at a precise time in a given tissue. The elimination of supernumerary pigment or inter-ommatidial cells (IOCs) depends on cell-cell communication and is necessary for the formation of the honeycomb-like structure of the Drosophila eye. However, the mechanisms occurring during pupal development and controlling apoptosis of superfluous IOC in space and time remain unclear. Here, we found that split-ends (spen) is required for IOC survival at the time of removal of superfluous IOCs. Loss of spen function leads to abnormal removal of IOCs by apoptosis. We show that spen is required non-autonomously in cone cells for the survival of IOCs by positively regulating the Spitz/EGFR pathway. We propose that Spen is an important survival factor that ensures spatial control of the apoptotic wave that is necessary for the correct patterning and formation of the Drosophila eye.

TGF-α ligands can substitute for the neuregulin Vein in Drosophila development

ErbB receptors, including the epidermal growth factor receptor (Egfr), are activated by EGF ligands to govern cell proliferation, survival, migration and differentiation. The different EGF-induced cell responses in development are regulated by deployment of multiple ligands. These inputs, however, engage only a limited number of intracellular pathways and are thought to elicit specific responses by regulating the amplitude or duration of the intracellular signal. The single Drosophila Egfr has four ligands: three of the TGF-α-type and a single neuregulin-like called vein (vn). Here, we used mutant combinations and gene replacement to determine the constraints of ligand specificity in development. Mutant analysis revealed extensive ligand redundancy in embryogenesis and wing development. Surprisingly, we found that the essential role of vn in development could be largely replaced by expression of any TGF-α ligand, including spitz (spi), in the endogenous vn pattern. vn mutants die as white undifferentiated pupae, but the rescued individuals showed global differentiation of adult body parts. Spi is more potent than Vn, and the best morphological rescue occurred when Spi expression was reduced to achieve an intracellular signaling level comparable to that produced by Vn. Our results show that the developmental repertoire of a strong ligand like Spi is flexible and at the appropriate level can emulate the activity of a weak ligand like Vn. These findings align with a model whereby cells respond similarly to an equivalent quantitative level of an intracellular signal generated by two distinct ligands regardless of ligand identity.

Update on Molecular Pathology of Cutaneous Melanocytic Lesions: What is New in Diagnosis and Molecular Testing for Treatment?

In this article, we give an update on recent findings regarding molecular pathology in cutaneous melanocytic tumors. The focus lies on use of genetics in the diagnosis of distinct subtypes of spitzoid tumors that are often characterized by specific phenotypic–genotypic alterations that can frequently be recognized by adequate histological examination. Typical illustrating cases are given in order to increase recognition of these lesions in daily dermatopathology practice. New molecular findings in the pathogenesis of congenital melanocytic tumors and neurocutaneous melanosis are reviewed. In addition, use of mutation analysis in the differential diagnosis of melanoma metastasis is discussed. Finally, application of mutation analysis in targeted therapy in advanced melanoma with advantages of new techniques such as next generation sequencing is described.

Trafficking of the EGFR ligand Spitz regulates its signaling activity in polarized tissues

Epidermal growth factor receptor (EGFR) ligands undergo a complex series of processing events during their maturation to active signaling proteins. Like its mammalian homologs, the predominant Drosophila EGFR ligand Spitz is produced as a transmembrane pro-protein. In the secretory pathway, Spitz is cleaved within its transmembrane domain to release the extracellular signaling domain. This domain is modified with an N-terminal palmitate group that tethers it to the plasma membrane. We found that the pro-protein can reach the cell surface in the absence of proteolysis, but that it fails to activate the EGFR. To address why the transmembrane pro-protein is inactive, whereas membrane association through the palmitate group promotes activity, we generated a panel of chimeric constructs containing the Spitz extracellular region fused to exogenous transmembrane proteins. Although the orientation of the EGF domain and its distance from the plasma membrane varies in these chimeras, they are all active in vivo. Thus, tethering Spitz to the membrane via a transmembrane domain at either terminus does not prevent activity. Conversely, removing the N-terminal palmitate group from the C-terminally tethered pro-protein does not render it active. Furthermore, we show that the Spitz transmembrane pro-protein can activate the EGFR in a tissue culture assay, indicating that its failure to signal in vivo is not due to structural features. In polarized imaginal disc cells, unprocessed Spitz pro-protein localizes to apical puncta, whereas the active chimeric Spitz constructs are basolaterally localized. Taken together, our data support the model that localized trafficking of the pro-protein restricts its ability to activate the receptor in polarized tissues.