In Situ Protein Expression Analysis of Melanocyte Differentiation Antigen TRP1 (Tyrosinase-Related Protein-1).

ABSTRACT: Melanocyte differentiation antigens refer to molecules expressed in cells of melanocytic lineage such as gp100/PMEL, tyrosinase, and Melan-A. Corresponding antibodies such as HMB45, T311, and A103 have become key immunohistochemical tools in surgical pathology for the diagnosis of pigmented and related lesions. Little is known about tyrosinase-related protein 1 (TRP1), another melanocyte differentiation antigen, which is an enzymatic component of melanogenesis and known as the brown locus in mice. In this study, we tested several commercial reagents to TRP1 and identified one clone, EPR13063, which we further characterized by testing its specificity and usefulness for surgical pathology. Subsequently, we analyzed the expression of TRP1 in panels of normal tissues and tumors. TRP1 is regularly expressed in normal skin and in cutaneous nevi predominantly present in junctional and to a lesser extent in dermal nevocytes. In melanoma, TRP1 is present in 100% and 44% of primary and metastatic melanomas, respectively. TRP1 was absent in 5 desmoplastic melanomas but heterogeneously present in 9 of 11 PEComas/angiomyolipomas. No TRP1 was found in neoplasms of nonmelanocytic lineage. We demonstrate that EPR13063 is a valuable reagent for the analysis of TRP1 expression in archival surgical pathology material. The TRP1 expression pattern in melanocytic and related lesions appears to parallel other melanocyte differentiation antigens with a higher incidence in primary and a lower incidence in metastatic melanomas.

Increase in forest structural complexity along a precipitation gradient is mediated by partial harvests in temperate Patagonian forests.

Increasing forest structural complexity is becoming a common goal in forestry worldwide. However, the lack of empirical quantification clouds its implementation. Here we quantified the long-term effects (> 30 y) of partial harvest on stand structural complexity and net primary productivity using the east-west precipitation gradient (318-2508 mm, mean annual precipitation-MAP) of western Patagonian as a study system. In this gradient, pairs of 1-ha plots on 20 sites (20 plots harvested and 20 plots unharvested) were installed. In each plot terrestrial laser scanning was used to quantify the stand structural complexity index (SSCI), and Sentinel satellite images to obtain the Enhanced Vegetation Index (EVI: proxy of net primary productivity). Generalized linear mixed-effect models were used to relate SSCI to MAP and EVI to SSCI, with harvesting as indicator variable, and site as random variable (two plots nested to same precipitation). Results showed that harvested plots on mesic-to-humid sites (but not on dry sites) had higher SSCI and EVI values compared to unharvested plots, likely due to a greater vertical canopy packing. These results show the influence of precipitation on SSCI, which resulted in a more diversified stand structure and higher EVI. Such insights support site-specific management aimed to increase forest structural complexity.

Phenotypic screening of seed retention and histological analysis of the abscission zone in Festuca pratensis and Lolium perenne.

BACKGROUND: Seed retention is the basic prerequisite for seed harvest. However, only little breeding progress has been achieved for this trait in the major forage grasses. The aim of this study was to evaluate the potential of plant genetic resources of the important fodder grasses Festuca pratensis Huds. and Lolium perenne L. as source for seed retention in the breeding process. Furthermore, the morphology of the abscission zone, where shattering occurs, was studied on the cell tissue level in different developmental stages of contrasting accessions. RESULTS: 150 and 286 accessions of Festuca pratensis and Lolium perenne were screened for seed retention, respectively. Contrasting accessions were selected to be tested in a second year. We found a great variation in seed retention in Festuca pratensis and Lolium perenne, ranging from 13 to 71% (average: 35%) and 12 to 94% (average: 49%), respectively, in the first year. Seed retention was generally lower in the second year. Cultivars were within the accessions with highest seed retention in Festuca pratensis, but had lower seed retention than ecotypes in Lolium perenne. Field-shattered seeds had a lower thousand grain weight than retained seeds. Cell layers of the abscission zone appeared already in early seed stages and were nested within each other in accessions with high seed retention, while there were two to three superimposed layers in accessions with low seed retention. CONCLUSIONS: Plant genetic resources of Lolium perenne might be a valuable source for breeding varieties with high seed retention. However, simultaneous selection for high seed weight is necessary for developing successful commercial cultivars.

Extramammary Paget Disease. Part I. Epidemiology, Pathogenesis, Clinical Features, and Diagnosis.

Extramammary Paget disease (EMPD) is a rare skin cancer of apocrine-rich skin that mimics common inflammatory and infectious dermatoses, leading to delays in diagnosis and increased patient morbidity. Better clinical recognition of this entity, multidisciplinary patient assessment, and deeper understanding of the underlying pathophysiology are essential to improve patient care and disease outcomes. It is important to distinguish primary intraepithelial/micro-invasive EMPD from invasive EMPD or cases with adenocarcinoma arising within EMPD. This 2-part continuing medical education series provides a complete picture of EMPD. Part 1 of this continuing medical education series reviews the epidemiology, oncogenesis, clinical and histopathologic presentation, workup, and prognosis of this rare cancer.

Population genomics and epigenomics of Spirodela polyrhiza provide insights into the evolution of facultative asexuality.

Many plants are facultatively asexual, balancing short-term benefits with long-term costs of asexuality. During range expansion, natural selection likely influences the genetic controls of asexuality in these organisms. However, evidence of natural selection driving asexuality is limited, and the evolutionary consequences of asexuality on the genomic and epigenomic diversity remain controversial. We analyzed population genomes and epigenomes of Spirodela polyrhiza, (L.) Schleid., a facultatively asexual plant that flowers rarely, revealing remarkably low genomic diversity and DNA methylation levels. Within species, demographic history and the frequency of asexual reproduction jointly determined intra-specific variations of genomic diversity and DNA methylation levels. Genome-wide scans revealed that genes associated with stress adaptations, flowering and embryogenesis were under positive selection. These data are consistent with the hypothesize that natural selection can shape the evolution of asexuality during habitat expansions, which alters genomic and epigenomic diversity levels.

Mixed histiocytic neoplasms: A multicentre series revealing diverse somatic mutations and responses to targeted therapy.

Histiocytic neoplasms are diverse clonal haematopoietic disorders, and clinical disease is mediated by tumorous infiltration as well as uncontrolled systemic inflammation. Individual subtypes include Langerhans cell histiocytosis (LCH), Rosai-Dorfman-Destombes disease (RDD) and Erdheim-Chester disease (ECD), and these have been characterized with respect to clinical phenotypes, driver mutations and treatment paradigms. Less is known about patients with mixed histiocytic neoplasms (MXH), that is two or more coexisting disorders. This international collaboration examined patients with biopsy-proven MXH with respect to component disease subtypes, oncogenic driver mutations and responses to conventional (chemotherapeutic or immunosuppressive) versus targeted (BRAF or MEK inhibitor) therapies. Twenty-seven patients were studied with ECD/LCH (19/27), ECD/RDD (6/27), RDD/LCH (1/27) and ECD/RDD/LCH (1/27). Mutations previously undescribed in MXH were identified, including KRAS, MAP2K2, MAPK3, non-V600-BRAF, RAF1 and a BICD2-BRAF fusion. A repeated-measure generalized estimating equation demonstrated that targeted treatment was statistically significantly (1) more likely to result in a complete response (CR), partial response (PR) or stable disease (SD) (odds ratio [OR]: 17.34, 95% CI: 2.19-137.00, p = 0.007), and (2) less likely to result in progression (OR: 0.08, 95% CI: 0.03-0.23, p < 0.0001). Histiocytic neoplasms represent an entity with underappreciated clinical and molecular diversity, poor responsiveness to conventional therapy and exquisite sensitivity to targeted therapy.

Towards a standardized reporting of the impact of magnetic resonance imaging on the decision-making of thoracolumbar fractures without neurological deficit: Conceptual framework and proposed methodology.

Introduction: A recent meta-analysis showed that only four prior studies have shown that magnetic resonance imaging (MRI) can change the fracture classification in 17% and treatment decisions in 22% of cases. However, previous studies showed a wide methodological variability regarding the study population, the definition of posterior ligamentous complex (PLC) injury, and outcome measures. Research question: How can we standardize the reporting of the impact of MRI for neurologically intact patients with thoracolumbar fractures? Material and methods: All available literature regarding the impact of MRI on thoracolumbar fracture classification or decision-making were reviewed. Estimating the impact of MRI on the TLFs' classification is an exercise of analyzing the CTs' accuracy for PLC injury against MRI as a ''Gold standard''and should follow standardized checklists such as the Standards for the Reporting of Diagnostic Accuracy Studies. Additionally, specific issues related to TLFs should be addressed. Results: A standardized approach for reporting the impact of MRI in neurologically intact TLF patients was proposed. Regarding patient selection, restricting the inclusion of neurologically intact patients with A- and B-injuries is crucial. Image interpretation should be standardized regarding imaging protocol and appropriate criteria for PLC injury. The impact of MRI can be measured by either the rate of change in fracture classification or treatment decisions; the cons and pros of each measure is thoroughly discussed. Discussion and conclusion: We proposed a structured methodology for examining the impact of MRI on neurologically intact patients with TLFs, focusing on appropriate patient selection, standardizing image analysis, and clinically relevant outcome measures.

Rigid spine injuries - A comprehensive review on diagnostic and therapeutic challenges.

Injuries to the rigid spine have a distinguished position in the broad spectrum of spinal injuries due to altered biomechanical properties. The rigid spine is more prone to fractures. Two ossification bone disorders that are of particular interest are Ankylosing Spondylitis (AS) and Diffuse Idiopathic Skeletal Hyperostosis (DISH). DISH is a non-inflammatory condition that leads to an anterolateral ossification of the spine. AS on the other hand is a chronic inflammatory disease that leads to cortical bone erosions and spinal ossifications. Both diseases gradually induce stiffening of the spine. The prevalence of DISH is age-related and is therefore higher in the older population. Although the prevalence of AS is not age-related the occurrence of spinal ossification is higher with increasing age. This association with age and the aging demographics in industrialized nations illustrate the need for medical professionals to be adequately informed and prepared. The aim of this narrating review is to give an overview on the diagnostic and therapeutic measures of the ankylosed spine. Because of highly unstable fracture configurations, injuries to the rigid spine are highly susceptible to neurological deficits. Diagnosing a fracture of the ankylosed spine on plain radiographs can be challenging. Moreover, since 8% of patients with ankylosing spine disorders (ASD) have multiple non-contagious fractures, a CT scan of the entire spine is highly recommended as the primary diagnostic tool. There are no consensus-based guidelines for the treatment of spinal fractures in ASD. The presence of neurological deficit or unstable fractures are absolute indications for surgical intervention. If conservative therapy is chosen, patients should be monitored closely to ensure that secondary neurologic deterioration does not occur. For the fractures that have to be treated surgically, stabilization of at least three segments above and below the fracture zone is recommended. These fractures mostly are treated via the posterior approach. Patients with AS or DISH share a significant risk for complications after a traumatic spine injury. The most frequent complications for patients with thoracolumbar burst fractures are respiratory failure, pseudoarthrosis, pneumonia, and implant failure.

The Impact of Next-generation Sequencing on Interobserver Agreement and Diagnostic Accuracy of Desmoplastic Melanocytic Neoplasms.

Next-generation sequencing (NGS) is increasingly being utilized as an ancillary tool for diagnostically challenging melanocytic neoplasms. It is incumbent upon the pathology community to perform studies assessing the benefits and limitations of these tools in specific diagnostic scenarios. One of the most challenging diagnostic scenarios faced by skin pathologists involves accurate diagnosis of desmoplastic melanocytic neoplasms (DMNs). In this study, 20 expert melanoma pathologists rendered a diagnosis on 47 DMNs based on hematoxylin and eosin sections with demographic information. After submitting their diagnosis, the experts were given the same cases, but this time with comprehensive genomic sequencing results, and asked to render a diagnosis again. Identification of desmoplastic melanoma (DM) improved by 7%, and this difference was statistically significant ( P <0.05). In addition, among the 15 melanoma cases, in the pregenomic assessment, only 12 were favored to be DM by the experts, while after genomics, this improved to 14 of the cases being favored to be DM. In fact, some cases resulting in metastatic disease had a substantial increase in the number of experts recognizing them as DM after genomics. The impact of the genomic findings was less dramatic among benign and intermediate-grade desmoplastic tumors (BIDTs). Interobserver agreement also improved, with the Fleiss multirater Kappa being 0.36 before genomics to 0.4 after genomics. NGS has the potential to improve diagnostic accuracy in the assessment of desmoplastic melanocytic tumors. The degree of improvement will be most substantial among pathologists with some background and experience in bioinformatics and melanoma genetics.

BRAF Mutated and Morphologically Spitzoid Tumors, a Subgroup of Melanocytic Neoplasms Difficult to Distinguish From True Spitz Neoplasms.

Drivers of Spitz neoplasms include activating point mutations in HRAS and Spitz-associated genomic fusions. It has become evident that some BRAF -mutated melanocytic neoplasms can morphologically mimic Spitz tumors (STs). These have been termed BRAF mutated and morphologically spitzoid (BAMS). In this study, 17 experts from the International Melanoma Pathology Study Group assessed 54 cases which included 40 BAMS and 14 true STs. The participants reviewed the cases blinded to the genomic data and selected among several diagnostic options, including BAMS, ST, melanoma, and other. A total of 38% of all diagnostic selections in the BAMS cases were for BAMS, whereas 32% were for ST. In 22 of the BAMS cases, the favored diagnosis was BAMS, whereas in 17 of the BAMS cases, the favored diagnosis was ST. Among the 20 cases in the total group of 54 with the highest number of votes for ST, half were BAMS. Of BAMS, 75% had a number of votes for ST that was within the SD of votes for ST seen among true ST cases. There was poor interobserver agreement for the precise diagnosis of the BAMS (kappa = 0.16) but good agreement that these cases were not melanoma (kappa = 0.7). BAMS nevi/tumors can closely mimic Spitz neoplasms. Expert melanoma pathologists in this study favored a diagnosis of ST in nearly half of the BAMS cases. There are BAMS cases that even experts cannot morphologically distinguish from true Spitz neoplasms.

ATOH1, TFAP2B, and CEACAM6 as Immunohistochemical Markers to Distinguish Merkel Cell Carcinoma and Small Cell Lung Cancer.

Merkel cell carcinoma (MCC) and small cell lung cancer (SCLC) can be histologically similar. Immunohistochemistry (IHC) for cytokeratin 20 (CK20) and thyroid transcription factor 1 (TTF-1) are commonly used to differentiate MCC from SCLC; however, these markers have limited sensitivity and specificity. To identify new diagnostic markers, we performed differential gene expression analysis on transcriptome data from MCC and SCLC tumors. Candidate markers included atonal BHLH transcription factor 1 (ATOH1) and transcription factor AP-2ß (TFAP2B) for MCC, as well as carcinoembryonic antigen cell adhesion molecule 6 (CEACAM6) for SCLC. Immunostaining for CK20, TTF-1, and new candidate markers was performed on 43 MCC and 59 SCLC samples. All three MCC markers were sensitive and specific, with CK20 and ATOH1 staining 43/43 (100%) MCC and 0/59 (0%) SCLC cases and TFAP2B staining 40/43 (93%) MCC and 0/59 (0%) SCLC cases. TTF-1 stained 47/59 (80%) SCLC and 1/43 (2%) MCC cases. CEACAM6 stained 49/59 (83%) SCLC and 0/43 (0%) MCC cases. Combining CEACAM6 and TTF-1 increased SCLC detection sensitivity to 93% and specificity to 98%. These data suggest that ATOH1, TFAP2B, and CEACAM6 should be explored as markers to differentiate MCC and SCLC.

Validation of the AO Spine CROST (Clinician Reported Outcome Spine Trauma) in the clinical setting.

PURPOSE: To evaluate feasibility, internal consistency, inter-rater reliability, and prospective validity of AO Spine CROST (Clinician Reported Outcome Spine Trauma) in the clinical setting. METHODS: Patients were included from four trauma centers. Two surgeons with substantial amount of experience in spine trauma care were included from each center. Two separate questionnaires were administered at baseline, 6-months and 1-year: one to surgeons (mainly CROST) and another to patients (AO Spine PROST-Patient Reported Outcome Spine Trauma). Descriptive statistics were used to analyze patient characteristics and feasibility, Cronbach's α for internal consistency. Inter-rater reliability through exact agreement, Kappa statistics and Intraclass Correlation Coefficient (ICC). Prospective analysis, and relationships between CROST and PROST were explored through descriptive statistics and Spearman correlations. RESULTS: In total, 92 patients were included. CROST showed excellent feasibility results. Internal consistency (α = 0.58-0.70) and reliability (ICC = 0.52 and 0.55) were moderate. Mean total scores between surgeons only differed 0.2-0.9 with exact agreement 48.9-57.6%. Exact agreement per CROST item showed good results (73.9-98.9%). Kappa statistics revealed moderate agreement for most CROST items. In the prospective analysis a trend was only seen when no concerns at all were expressed by the surgeon (CROST = 0), and moderate to strong positive Spearman correlations were found between CROST at baseline and the scores at follow-up (rs = 0.41-0.64). Comparing the CROST with PROST showed no specific association, nor any Spearman correlations (rs = -0.33-0.07). CONCLUSIONS: The AO Spine CROST showed moderate validity in a true clinical setting including patients from the daily clinical practice.

Using Equipoise to Determine the Radiographic Characteristics Leading to Agreement on Best Treatment for Thoracolumbar Burst Fractures Without Neurologic Deficits.

STUDY DESIGN: Retrospective analysis of prospectively collected data. OBJECTIVES: Our goal was to assess radiographic characteristics associated with agreement and disagreement in treatment recommendation in thoracolumbar (TL) burst fractures. METHODS: A panel of 22 AO Spine Knowledge Forum Trauma experts reviewed 183 cases and were asked to: (1) classify the fracture; (2) assess degree of certainty of PLC disruption; (3) assess degree of comminution; and (4) make a treatment recommendation. Equipoise threshold used was 77% (77:23 distribution of uncertainty or 17 vs 5 experts). Two groups were created: consensus vs equipoise. RESULTS: Of the 183 cases reviewed, the experts reached full consensus in only 8 cases (4.4%). Eighty-one cases (44.3%) were included in the agreement group and 102 cases (55.7%) in the equipoise group. A3/A4 fractures were more common in the equipoise group (92.0% vs 83.7%, P < .001). The agreement group had higher degree of certainty of PLC disruption [35.8% (SD 34.2) vs 27.6 (SD 27.3), P < .001] and more common use of the M1 modifier (44.3% vs 38.3%, P < .001). Overall, the degree of comminution was slightly higher in the equipoise group [47.8 (SD 20.5) vs 45.7 (SD 23.4), P < .001]. CONCLUSIONS: The agreement group had a higher degree of certainty of PLC injury and more common use of M1 modifier (more type B fractures). The equipoise group had more A3/A4 type fractures. Future studies are required to identify the role of comminution in decision making as degree of comminution was slightly higher in the equipoise group.

What Factors Influence Surgeons in Decision-Making in Thoracolumbar Burst Fractures? A Survey-Based Investigation of a Panel of Spine Surgery Experts.

STUDY DESIGN: Cross-sectional survey study. OBJECTIVE: To investigate factors affecting decision-making in thoracolumbar burst-fractures without neurologic deficit. METHODS: A 40-question survey addressing expert-related, economic, and radiological factors was distributed to 30 international trauma experts. Descriptive statistics were used to assess the impact of these factors on operative or non-operative management preferences. RESULTS: Out of 30 experts, 27 completed the survey. The majority of respondents worked at level 1 trauma centers (81.5%) within university settings (77.8%). They were primarily orthopedic surgeons (66.7%) and had over 10 years of experience (70.4%). About 81% found distinguishing between A3 and A4 fractures relevant for decision-making. Most experts (59%) treated A3 fractures non-surgically, while only 30% treated A4 fractures conservatively. Compensation systems did not influence treatment recommendations, and hospital measures promoting surgeries did not significantly affect distribution. Radiological factors, such as local kyphosis (25/27), fracture comminution (23/27), overall sagittal balance (21/27), and spinal canal narrowing (20/27), influenced decisions. CONCLUSION: Incomplete burst fractures (A3) are predominantly treated non-surgically, while complete burst fractures (A4) are primarily treated surgically. Compensation, third-party incentives, and outpatient care did not significantly impact decision-making. Radiological factors beyond the AO Spine thoracolumbar classification system seem to be essential and warrant further evaluation.

Nuclear and mitochondrial genetic variants associated with mitochondrial DNA copy number.

Mitochondrial DNA copy number (mtDNA-CN) is a biomarker for mitochondrial dysfunction associated with several diseases. Previous genome-wide association studies (GWAS) have been performed to unravel underlying mechanisms of mtDNA-CN regulation. However, the identified gene regions explain only a small fraction of mtDNA-CN variability. Most of this data has been estimated from microarrays based on various pipelines. In the present study we aimed to (1) identify genetic loci for qPCR-measured mtDNA-CN from three studies (16,130 participants) using GWAS, (2) identify potential systematic differences between our qPCR derived mtDNA-CN measurements compared to the published microarray intensity-based estimates, and (3) disentangle the nuclear from mitochondrial regulation of the mtDNA-CN phenotype. We identified two genome-wide significant autosomal loci associated with qPCR-measured mtDNA-CN: at HBS1L (rs4895440, p = 3.39 × 10-13) and GSDMA (rs56030650, p = 4.85 × 10-08) genes. Moreover, 113/115 of the previously published SNPs identified by microarray-based analyses were significantly equivalent with our findings. In our study, the mitochondrial genome itself contributed only marginally to mtDNA-CN regulation as we only detected a single rare mitochondrial variant associated with mtDNA-CN. Furthermore, we incorporated mitochondrial haplogroups into our analyses to explore their potential impact on mtDNA-CN. However, our findings indicate that they do not exert any significant influence on our results.

Spindle cell porocarcinoma with a novel YAP1::MAML3 fusion.

Porocarcinomas are rare sweat gland cancers representing the malignant counterpart to benign poromas. Their diagnosis can be challenging, especially in the absence of an associated poroma or when the tumor is poorly differentiated. Since recurrent YAP1::MAML2 and YAP1::NUTM1 fusions have been identified in poroid tumors, molecular studies provide an opportunity to support the diagnosis in challenging cases. We describe a case of a female patient in her early 90s, with a polypoid mass of the hip. Histopathologically, there was a poorly differentiated malignant spindle cell tumor adjacent to a poroma. Because of the close association with a poroma and immunoreactivity for p40, a diagnosis of spindle cell porocarcinoma was rendered, which was further supported by YAP1 immunohistochemical studies. Antibodies targeting both the N-terminus and C-terminus confirmed YAP1 rearrangement in both the poroma and the spindle cell neoplasm. Subsequent targeted RNA sequencing revealed a YAP1::MAML3 gene fusion. MAML3 has previously not yet been reported as a YAP1 fusion partner in porocarcinoma. With the illustration of a rare spindle cell variant of porocarcinoma and the identification of a novel gene fusion, this case report expands the spectrum of morphologic and genomic aberrations associated with porocarcinoma.

Mother trees, altruistic fungi, and the perils of plant personification.

There are growing doubts about the true role of the common mycorrhizal networks (CMN or wood wide web) connecting the roots of trees in forests. We question the claims of a substantial carbon transfer from 'mother trees' to their offspring and nearby seedlings through the CMN. Recent reviews show that evidence for the 'mother tree concept' is inconclusive or absent. The origin of this concept seems to stem from a desire to humanize plant life but can lead to misunderstandings and false interpretations and may eventually harm rather than help the commendable cause of preserving forests. Two recent books serve as examples: The Hidden Life of Trees and Finding the Mother Tree.

A cutaneous epithelioid vascular tumor harboring a TPM3::ALK fusion.

Substantial progress has been made in understanding the molecular pathways associated with vascular tumors over the last two decades. In addition to mutations and copy number aberrations, fusions have emerged as significant contributors to the pathogenesis of a notable subset of vascular tumors. In this report, we present a case of an unusual intradermal vascular tumor with epithelioid cytomorphology. Immunohistochemistry revealed diffuse positivity for CD31, ERG and Factor VIII, supporting its endothelial lineage. RNA sequencing (ArcherFusion Plex) revealed the presence of an in-frame fusion between the genes TPM3 Exon 8 and ALK Exon 20. Immunohistochemistry confirmed ALK expression by the endothelial cells. To our knowledge, this is the first documented case of a vascular tumor harboring an ALK fusion. It may fall within the spectrum of epithelioid hemangiomas; nevertheless, we cannot definitively exclude the possibility of it being a distinct and potentially unique benign entity on its own.

Perifollicular linear projections: A dermatoscopic criterion for the diagnosis of lentigo maligna on the face.

BACKGROUND: Lentigo maligna (LM) can mimic benign, flat, pigmented lesions and can be challenging to diagnose. OBJECTIVE: To describe a new dermatoscopic feature termed "perifollicular linear projections (PLP)" as a diagnostic criterion for LM on the face. METHODS: Retrospective study on reflectance confocal microscopy and dermatoscopy images of flat facial pigmented lesions originating from 2 databases. PLP were defined as short, linear, pigmented projections emanating from hair follicles. Dermatoscopy readers were blinded to the final histopathologic diagnosis. RESULTS: From 83 consecutive LMs, 21/83 (25.3%) displayed "bulging of hair follicles" on reflectance confocal microscopy and 18 of these 21 (85.7%), displayed PLP on dermatoscopy. From a database of 2873 consecutively imaged and biopsied lesions, 252 flat-pigmented facial lesions were included. PLP was seen in 47/76 melanomas (61.8%), compared with 7/176 lesions (3.9%) with other diagnosis (P < .001). The sensitivity was 61.8% (95% CI, 49.9%-72.7%), specificity 96.0% (95% CI, 92.9%-98.4%). PLP was independently associated with LM diagnosis on multivariate analysis (OR 26.1 [95% CI, 9.6%-71.0]). LIMITATIONS: Retrospective study. CONCLUSION: PLP is a newly described dermatoscopic criterion that may add specificity and sensitivity to the early diagnosis of LM located on the face. We postulate that PLP constitutes an intermediary step in the LM progression model.