[Collision tumours in skin: usually an incidental finding. A retrospective study with literature revision]. / Tumores de colisión en la piel: un hallazgo incidental en la mayoría de los casos. Estudio retrospectivo y revisión de la literatura.

A collision tumour (CT) is a neoplastic lesion comprised of two or more distinct cell populations that maintain distinct borders. Mostly, these are incidental findings in skin biopsies, whose pathologic mechanism and prevalence remain unknown, with few references among literature. Here, we present a retrospective study of CT, diagnosed by a dermatopathologist in our hospital between 2019-2022. Lesions have been defined individually and organized into three categories: benign-benign (BB), benign-malignant (BM) and malignant-malignant (MM). A total of 108 CT were diagnosed (1,4% of the biopsies from the dermatopathologist during this period), from which BM was the most frequent collision (48,5%). Globally, basal cell carcinoma (BCC) was the main malignant lesion and melanocytic nevus (MN) the main benign lesion. We have used the software Stata 14.2 in order to analyse results, and we have detected a statistically significant difference between age and collision type.

Incidence of neurocutaneous melanosis in Japanese pediatric patients with congenital melanocytic nevi.

Neurocutaneous melanosis (NCM) is a rare, non-hereditary neurocutaneous disorder characterized by excessive melanocytic proliferation in the skin and central nervous system. As no major studies have covered the incidence of NCM among Japanese patients with congenital melanocytic nevi (CMN), we prospectively investigated the incidence of NCM among Japanese patients who underwent initial treatment for CMN. The relationship of CMN and NCM was also investigated. Japanese pediatric patients with CMN under 1 year of age were included between January 2020 and November 2022, and all patients underwent brain MRI to check for NCM in this study. NCM lesions were most frequently seen in the amygdala, followed by the cerebellum, brainstem, and cerebral hemispheres. NCM was diagnosed on brain MRI in 31.6% of the 38 patients with CMN and in 25.0% of patients with no prior examination or treatment. Distribution and size of CMN, number of satellite nevi, rugosity and nodules were strongly associated with the existence of NCM, and these findings may guide a future registry study with a large cohort of CMN patients.

Acral Melanocytic Nevi in a High-Risk Population: Prevalence, Clinical Characteristics and Dermatoscopic Patterns.

BACKGROUND: The prevalence of acral nevi and their dermatoscopic patterns have been mainly studied in Asian populations. Few data exist on the prevalence and clinico-dermatoscopic morphology of acral nevi in white populations. OBJECTIVES: The aim of this study was to assess the prevalence of acral nevi and evaluate their features in a cohort of Caucasian individuals at high risk for skin cancer. METHODS: We prospectively examined the palms and soles of 680 high-risk patients who underwent total body clinical and dermatoscopic documentation, as a part of their routine follow-up, between January 2016 and March 2020 at a skin cancer referral center in Greece. RESULTS: Overall, 334 acral lesions were detected in 217 (37.0%) of 585 patients in the study. The presence of acral nevi was associated with 2.6 higher odds of a total nevus count higher than 50 (OR: 2.6, p < 0.05, confidence intervals [CI]: 1.11-6.09). Of 334 acral nevi, 65.0% were clinically flat and 35.0% were clinically palpable. Palpable lesion had 19-fold higher probability of being located on the sole (OR: 19.44, p < 0.05, CI: 3.91-96.7). The parallel furrow pattern was present in 147 lesions (44.0%). In 76 lesions (22.8%), we observed a previously undefined pattern consisting of wavy lines, which was correlated with clinically palpable lesions (p < 0.001). The third most common pattern was homogeneous (10.5%), followed by the fibrillar (8.7%), the lattice-like (7.2%), the reticular (3.6%), and globular (3.3%). CONCLUSION: We observed a higher prevalence of benign acral melanocytic lesions than expected, probably related to our cohort selection of patients at high risk for developing skin cancer. Our study confirms the previously described dermatoscopic patterns and provides novel insights into the dermatoscopic morphology of acral palpable nevi, for which we described a new benign pattern consisting of wavy lines.

Focal melanocytic lesions of the oral mucosa: An epidemiological and morphological study.

OBJECTIVE: This study aimed to analyse the clinical and histopathological characteristics of focal oral melanocytic lesions in a Brazilian reference service in Oral and Maxillofacial Pathology. MATERIALS AND METHODS: A cross-sectional study was conducted over an 18-year period. Demographic data and clinical features were collected from the archives, and all biopsy specimens diagnosed as oral melanocytic lesions were retrieved and reviewed. RESULTS: We identified 339 melanocytic lesions. Of these, 191 were melanotic macules, 112 melanocytic nevi, 14 mucosal lentigo simplex, 12 melanomas, 9 solar lentigos, and 1 melanoacanthoma. Lesions occurred mostly in white-skinned (74.2%) women (65.2%). The main reported clinical aspect was the macule (67.4%), and the most affected site was the lip vermilion (25.4%), followed by the palate (22.9%). Melanomas were larger in size and were observed in older patients with an overall shorter time of onset. The most frequent subtypes of melanocytic nevi were intramucosal (44.6%), compound (24.1%), and blue nevus (20.5%). They showed a heterogeneous architectural pattern with the presence of the three cell types. CONCLUSION: The most frequent lesions are melanotic macule and nevus, especially the intramucosal subtype. Patients are usually white-skinned women presenting a small, long-lasting, macular lesion on the lip vermilion or palate.

Can the MOLES acronym and scoring system improve the management of patients with melanocytic choroidal tumours?

It can be difficult for practitioners to determine the likelihood of malignancy in melanocytic choroidal tumours. This author has therefore devised the MOLES acronym to highlight the most informative clinical features, which comprise mushroom shape, orange pigment, large size, enlargement, and subretinal fluid. Each of these is scored 0 if absent, 1 if subtle or uncertain, and 2 if present. Tumours are categorised as 'common naevus', 'low-risk naevus', 'high-risk naevus' and 'probable melanoma' according to whether the sum of these five scores is 0, 1, 2 or 3 or more, respectively. Tentative recommendations, subject to future studies, include: review of 'common naevi' by a community optometrist whenever the patient attends for another reason, such as a two-yearly 'check-up' (i.e., 'self-care'); non-urgent referral of patients with 'low-risk naevi' or 'high-risk naevi' to an ophthalmologist to plan long-term surveillance (i.e., determining the frequency of assessments and whether these should be undertaken by an ophthalmologist or a community optometrist); and urgent referral of patients with a MOLES score >2 (i.e., 'probable melanoma') to an ophthalmologist for immediate referral to an ocular oncologist if a suspicion of malignancy is confirmed. The MOLES system does not require assessment of internal acoustic reflectivity by ultrasonography. MOLES scores correlate well with diagnosis of choroidal naevi and melanomas by ocular oncologists; however, further evaluation of this aid in routine optometric practice and other situations is needed. MOLES should prevent unnecessary referral of patients with naevi for second opinion and non-essential monitoring of these patients at hospital eye services.

Comparison of phenotypic features in patients with single vs multiple primary cutaneous melanomas: a prospective single-center study.

BACKGROUND: There is sparse data regarding total body nevus count (TBNC), nevus count in specific locations, phenotypic factors, anthropometric indices, sunburn, and the relation to multiple primary cutaneous melanomas (MPCM) development. We aim to compare these variables in a cohort of patients diagnosed with single primary melanoma (SPM) and MPCM with histologic diagnoses of melanoma in situ, superficial spreading, and nodular melanoma in our clinic. METHODS: Prospective observational studies for the evaluation of nevus counts in biopsy-proven melanoma patients from 2017 to 2020 at Ankara University were conducted. Age, gender, family history of melanoma, increased sun exposure, nonmelanoma skin cancers (NMSC), height, sunburn history, TBNC, and nevi count in specific anatomical locations were evaluated by multivariate logistic regression analysis. RESULTS: A total number of 156 patients consisting of 22 MPCM and 134 SPM were included. Mean TBNC for SPM vs MPCM patients were 96.87 (SD ± 124.71) vs 247.00 (SD ± 261.58), respectively (P < 0.0001). TBNC was correlated to the left arm, trunk, lower extremity, and head and neck nevus counts but not with the right arm nevus count. Multiple regression analysis showed that having more than 10 nevi on the head and neck area is associated with MPCM (OR, 3.882 [95% CI, 1.084-13.899]). TBNC and nevus count in specific locations were found to be significantly higher in MPCM. CONCLUSION: The risk of MPCM was associated with having ≥10 nevi on the head and neck.

Motivos de derivación y características epidemiológicas de los pacientes atendidos en una consulta monográfica de dermatoscopia de un hospital terciario español / Reasons for Referral and Epidemiological Characteristics of Patients Seen at a Dedicated Dermoscopy Unit in a Spanish Tertiary Care Hospital

Las consultas monográficas de dermatoscopia digital están dirigidas a la población con alto riesgo de melanoma. Conocer los motivos de derivación a estas consultas, así como las características epidemiológicas de los pacientes permite optimizar los recursos sanitarios, y determinar qué pacientes se benefician más de esta técnica. Se analizaron los motivos de derivación y las características epidemiológicas de 413 pacientes atendidos en una consulta monográfica de dermatoscopia en un período de 10 años, y que presentaban al menos un criterio de alto riesgo de melanoma. También se analizó el número necesario de extirpaciones (NNE) por cada melanoma diagnosticado, sus características histológicas y las variables no ambientales se asociaron con su diagnóstico. Los motivos de derivación más frecuentes fueron: antecedentes de melanoma previo (21,5%), cambios detectados por el paciente o su familia (20%), hallazgos clínicos y/o dermatoscópicos sospechosos de malignidad (19,4%) y antecedentes familiares de melanoma (17,4%). Setenta y seis de las 178 lesiones extirpadas fueron melanomas, obteniendo un NNE de 2,34. La edad avanzada fue el único factor de riesgo que se asoció de forma estadísticamente significativa con el desarrollo de melanoma (AU)

Dedicated dermoscopy units assess individuals at high risk for melanoma. Understanding the reasons for referral to these units and the epidemiological profile of referred patients can help optimize health care resources and determine who benefits most from dermoscopic evaluation. We analyzed reasons for referral and epidemiological characteristics of 413 patients with at least 1 high-risk factor for melanoma seen at a dedicated dermoscopy unit over a period of 10 years. We also analyzed the number of necessary excisions (NNE) for each melanoma diagnosed, histologic features, and associations between nonenvironmental factors and diagnosis. The main reasons for referral were a past history of melanoma (21.5%), changes detected by the patient or a relative (20%), clinical and/or dermoscopic findings suggestive of malignancy (19.4%), and a family history of melanoma (17.4%). Seventy-six of the 178 excised lesions were melanomas (NNE per melanoma detected, 2.34). Older age was the only risk factor significantly associated with the development of melanoma (AU)

[Translated article] Reasons for Referral and Epidemiological Characteristics of Patients Seen at a Dedicated Dermoscopy Unit in a Spanish Tertiary Care Hospital / Motivos de derivación y características epidemiológicas de los pacientes atendidos en una consulta monográfica de dermatoscopia de un hospital terciario español

Dedicated dermoscopy units assess individuals at high risk for melanoma. Understanding the reasons for referral to these units and the epidemiological profile of referred patients can help optimize health care resources and determine who benefits most from dermoscopic evaluation. We analyzed reasons for referral and epidemiological characteristics of 413 patients with at least 1 high-risk factor for melanoma seen at a dedicated dermoscopy unit over a period of 10 years. We also analyzed the number of necessary excisions (NNE) for each melanoma diagnosed, histologic features, and associations between nonenvironmental factors and diagnosis. The main reasons for referral were a past history of melanoma (21.5%), changes detected by the patient or a relative (20%), clinical and/or dermoscopic findings suggestive of malignancy (19.4%), and a family history of melanoma (17.4%). Seventy-six of the 178 excised lesions were melanomas (NNE per melanoma detected, 2.34). Older age was the only risk factor significantly associated with the development of melanoma (AU)

Las consultas monográficas de dermatoscopia digital están dirigidas a la población con alto riesgo de melanoma. Conocer los motivos de derivación a estas consultas, así como las características epidemiológicas de los pacientes permite optimizar los recursos sanitarios, y determinar qué pacientes se benefician más de esta técnica. Se analizaron los motivos de derivación y las características epidemiológicas de 413 pacientes atendidos en una consulta monográfica de dermatoscopia en un período de 10 años, y que presentaban al menos un criterio de alto riesgo de melanoma. También se analizó el número necesario de extirpaciones (NNE) por cada melanoma diagnosticado, sus características histológicas y las variables no ambientales se asociaron con su diagnóstico. Los motivos de derivación más frecuentes fueron: antecedentes de melanoma previo (21,5%), cambios detectados por el paciente o su familia (20%), hallazgos clínicos y/o dermatoscópicos sospechosos de malignidad (19,4%) y antecedentes familiares de melanoma (17,4%). Setenta y seis de las 178 lesiones extirpadas fueron melanomas, obteniendo un NNE de 2,34. La edad avanzada fue el único factor de riesgo que se asoció de forma estadísticamente significativa con el desarrollo de melanoma (AU)

A review of nevus-associated melanoma: What is the evidence?

Cutaneous melanoma may have an adjacent nevus remnant on histological examination in 30% of cases (nevus-associated melanoma, NAM), while it may appear de novo, without a precursor lesion, in the remaining 70% of cases. Nevus-associated melanoma and the concept of acquired melanocytic nevi serving as precursors of melanoma has long been considered as a controversial topic. This controversy is, in part, due to their overall low rate of transformation to melanoma and scarce data on the natural history of progression. Another matter of debate regarded the possibility that the reported differences in NAM vs. de novo melanoma were due to an underestimation of NAM in thicker lesions due to obliteration of the nevus component by the tumour. During the last few years, several evidence has accumulated in order to address these controversies. In this review, we present a comprehensive synthesis of the epidemiological, clinical, dermoscopic and genetic findings in NAM, including thin NAM, compared to de novo melanoma. Answering the questions on nevus-associated melanoma may provide further insight into the classification of these tumours and disentangle their biology and route of development from that of de novo melanoma.

Neurological signs, symptoms and MRI abnormalities in patients with congenital melanocytic naevi and evaluation of routine MRI-screening: systematic review and meta-analysis.

BACKGROUND: A congenital melanocytic naevus (CMN) is a rare skin condition that can be associated with abnormalities of the central nervous system (CNS). These anomalies can sometimes cause severe complications, and rarely death. Adequate information about aetiology and management is therefore crucial. To identify how to monitor patients with CMN, we aimed to estimate the prevalence of neurological involvement in patients with CMN and to summarize what specific neurological signs and symptoms and MRI abnormalities are reported in the medical literature. In addition, we summarized and evaluated the recommendations regarding MRI-screening reported in the medical literature. METHODS: This review was registered in PROSPERO and reported according to the MOOSE checklist. A search was conducted in EMBASE (Ovid), PubMed, and the Cochrane Library. We included studies with 10 or more patients with CMN, reporting on neurological signs and symptoms or CNS MRI. Study selection, data extraction and methodological quality assessment were performed by two independent reviewers. A meta-analysis was used to assess the prevalence of neurological signs and symptoms. RESULTS: Out of 1287 studies, fourteen studies were eligible for inclusion of which eight were included in the meta-analysis. Neurological signs and symptoms prevalence was 7.04% (CI 95% 4.47-10.93%) in the meta-analysis group and 6.26% (95% CI 3.85-10%) in a subgroup of patients with a CMN > 6 cm, evaluated in seven studies. Neurodevelopmental delay and seizures were the most frequently reported signs and symptoms. CNS melanocytosis and hydrocephalus were the most frequently reported MRI abnormalities. It was not possible to estimate the increased risk of neurological involvement in patients with CMN due to low quality of evidence and clinical heterogeneity. CONCLUSION: Standardization in CMN studies and a multi-centre prospective study are needed to evaluate neurological involvement. Based on current literature, it is not possible to make strong recommendations on routine MRI-screening. For now, every clinical centre should decide on its own policy and weigh the advantages and disadvantages of routine MRI.

Risk of Malignant Transformation Arising From Giant Congenital Melanocytic Nevi: A 20-year Single-center Study.

BACKGROUND: Although giant congenital melanocytic nevus (GCMN) is regarded as premalignant, the incidence and risk factors of malignant transformation are controversial. OBJECTIVE: This study aimed to share the authors' surgical experience with GCMNs and provide data on their demographics, malignant transformation, and prognosis. METHODS: This single-center, consecutive study included 152 patients with GCMN who visited this center from March 2000 to February 2020. Their medical documentation was reviewed retrospectively, and the nevi were classified according to the size as follows: Group 1, 10 to 19.9 cm (n = 45); Group 2, 20 to 39.9 cm (n = 62); and Group 3, ≥40 cm (n = 45). RESULTS: Seven malignancies were found (4.6%; 4 melanomas, 2 rhabdomyosarcomas [RMS], and 1 malignant peripheral nerve sheath tumor [MPNST]). The risk increased according to the nevus size (2.2% in Group 1, 3.2% in Group 2, and 8.9% in Group 3) but the difference was not statistically significant (p = .3305). CONCLUSION: Malignant transformation from GCMN cannot be ignored. It can include transformation into melanoma, RMS, and MPNST. Early surgical resection and regular follow-up should be performed in patients with nevi ≥10 cm.

Choroidal melanocytic lesions in children: focal aggregates and melanocytosis.

PURPOSE: To investigate prevalence and age of onset of choroidal melanocytic lesions (other than nevi) in pediatric patients. METHODS: The pooled data of participants 6 months to 18 years of age in the Sydney Paediatric Eye Disease Study, the Sydney Myopia Study, and the Sydney Adolescent Vascular Eye Disease Study were reviewed retrospectively to identify children with choroidal melanocytic lesions. The clinical features and prevalence by age were assessed. RESULTS: From the pooled sample of 5,533 unique children, 39 cases of focal melanocytic aggregates and 22 cases of choroidal melanocytosis were identified, with overall prevalence of 0.70% and 0.40%, respectively. There was a statistically significant trend toward increased prevalence with increasing age. Both focal melanocytic aggregates and choroidal melanocytosis tended to be bilateral (100% and 86% respectively), brown in color, and temporally located in all cases. Amelanotic variants were not identified. Focal melanocytic aggregates were small (0.15-0.5 mm), whereas choroidal melanocytosis varied in size (5.0-20 mm). All focal melanocytic aggregates were characteristically located 4-5 mm temporal to the center of the fovea and were associated with linear nervelike (11 [28%]) or tortuous vessel like structures (10 [26%]). CONCLUSIONS: In this study, pooled data from large population studies revealed morphologic patterns of choroidal melanocytic lesions, other than nevus, that correlate with described clinical appearance in adults. The association of focal melanocytic aggregates with nervelike structures supports their embryologic origin along the migration path of uveal melanocytes.

Prevalence and Dermoscopic Patterns of Acral Melanocytic Nevi in Turkey.

Although nevi are frequently encountered in the acral region, very limited studies have reported their prevalence in specific populations. We aimed to determine the prevalence of acral nevi, their dermoscopic patterns, and evaluate patient awareness in a Turkish population. We prospectively examined 2644 patients admitted to the outpatient dermatology clinics between October 2016 and October 2017. The characteristics of the detected acral nevi and dermatoscopic images were recorded. A questionnaire of demographic characteristics was completed from all patients. Two hundred six of the 2644 patients had at least one acral nevus. Two hundred sixty nevi were examined. The general prevalence of acral nevi was 7.8%. Women were more likely to have acral nevi than men (8.7% vs. 6.3%; P=0.028). Moreover, darker-skinned patients were also had significantly more acral nevi (8.6% in skin type III-IV vs. 6.0% in skin type I-II; P<0.001). The prevalence of acral nevi was 9.4% before the age of 20, 9.5% in patients aged 20-40 years, and 4.6% after the age of 40. In addition, 51.5% of all nevi exhibited a parallel furrow, 13.5% were lattice-like, and 7.7% had a homogeneous pattern. The overall nevus awareness rate was 73.8% and was significantly higher in women at 78.3%. Our study is the first large-scale study of that showed the prevalence of acral nevi in Turkey. According to our study, the prevalence of acral nevi was higher in patients with female sex and darker skin type. We also found that the prevalence of acral nevi decreased over 40 years of age. The general awareness of nevi was higher in women.

Prevalence of nevi, atypical nevi, and lentigines in relation to tobacco smoking.

BACKGROUND: Melanocytic nevi have a complex evolution influenced by several endogenous and exogenous factors and are known risk factors for malignant melanoma. Interestingly, tobacco use seems to be inversely associated with melanoma risk. However, the association between tobacco use and nevi and lentigines has not yet been evaluated. METHODS: We investigated the prevalence of nevi, atypical nevi, and lentigines in relation to tobacco smoking in a cohort of 59 smokers and 60 age- and sex-matched nonsmokers, using a questionnaire and performing a total body skin examination by experts. RESULTS: No significant differences were detected between smokers and nonsmokers in the numbers of nevi, atypical nevi, and lentigines in sun-exposed areas (p = 0.966, 0.326, and 0.241, respectively) and in non-sun-exposed areas (p = 0.095, 0.351, and 0.546, respectively). CONCLUSION: Our results revealed no significant differences in the prevalence of nevi, atypical nevi, and lentigines between smokers and nonsmokers in sun-exposed and non-sun-exposed areas.

Demographic, clinical and dermoscopic features of melanocytic nevi on the scalp.

BACKGROUND: The scalp is a special anatomical area and dermoscopic findings of this region may significantly differ from other body parts. OBJECTIVE: To investigate and compare the clinical and dermoscopic patterns of scalp melanocytic nevi in patients ≤15 years of age and above, and to analyse their relevance to demographic features, atypical mole syndrome (AMS) and total body nevus count (TBNC). METHODS: In this retrospective cohort study, the clinical data and dermoscopic images of patients with scalp melanocytic nevi were retrieved, reviewed and analysed. Demographic, clinical and dermoscopic features were compared in patients ≤15 years of age and above. RESULTS: A total of 196 scalp melanocytic nevi in 126 patients (female/male:64/62; ≤15/>15 years of age: 49/77) with a median age of 18.5 years (range 0-72) were evaluated. Statistically, the globular pattern was significantly higher in all age groups, and the papillomatous pattern was significantly lower in patients ≤15 years of age (P = 0.008 and P = 0.005, respectively). The eclipse pattern was significantly higher, and the homogenous pattern was significantly lower in patients ≤15 years of age with AMS (P = 0.003 and P = 0.014, respectively). Finally, patients ≤15 years of age with 50 to 100 TBNC had a higher eclipse pattern than those with 0 to 25 TBNC. CONCLUSION: The findings of this retrospective study might implicate that children with eclipse pattern of scalp melanocytic nevi might be 'moley' in the future with an impending risk of AMS. This hypothesis requires confirmation in future prospective studies on a larger cohort of patients.

Are we born and do we die without nevi? A cross-sectional study.

BACKGROUND: It is well known that the number of nevi varies with age. However, there are a few data in the literature concerning total nevus count at different ages. The aim of this study was to assess and compare the total nevus count among different age groups. METHODS: The total nevus count was assessed in consecutive patients belonging to nine age groups. Median nevus count was calculated and compared for each age group. Multivariate logistic regression analysis was used to define the influence of sex and phototype on the association between nevus count and age. RESULTS: We enrolled 900 patients (461, 51.2% females), with a median age of 46 years and a total of 18,136 nevi. Significant differences were found in the median total nevus count among all age groups (P < 0.001), with a significant increase in the first two decades and a significant decrease after the age of 50 years. A similar trend was also observed in subgroups. The differences observed in the total body nevus count among age groups were independent of sex and phototype. CONCLUSIONS: We demonstrate that the total nevus count significantly increases during childhood and gradually decreases in the elderly.

Phenotypic Characteristics and Melanoma Thickness in Women.

Patients' phenotypic characteristics might be associated with melanoma aggressiveness, but the evidence is scarce. This study examined the associations be-tween pigmentary characteristics, naevi and melanoma thickness. Data from the Norwegian Women and Cancer (NOWAC) study were analysed. By 2014, 1,243 women were diagnosed with a primary melanoma, and 1,140 had information on thickness. Using ordinal logistic regression models, the probability of being diagnosed with a specific thickness category was calculated by pigmentary score and naevi. Fair pigmentary score was associated with thinner trunk melanomas (probabilities of being diagnosed with a tumour ≤1.0 mm thickness were 74%, 66%, and 51% for fair, medium and dark pigmentary scores, respectively), but not the other sites. High number of naevi was associated with thicker nodular melanoma (NM) but not with super-ficial spreading melanoma. These findings suggest the need for greater overall vigilance and skin checks among women with fair pigmentary score. The association between naevi and NM suggest possible biological mechanisms.

The utility of PRAME staining in identifying malignant transformation of melanocytic nevi.

BACKGROUND: PReferentially expressed Antigen in MElanoma (PRAME) immunohistochemical (IHC) staining is used to aid melanoma diagnosis. PRAME expression in nevus-associated melanoma (NAM) has not been evaluated. METHODS: PRAME IHC was applied to cases of NAM; staining for each population of melanocytes (benign and malignant) was graded based on the percentage of labeled cells. No labeling was graded 0, 1% to 25% labeling was 1+, 26% to 50% was 2+, 51% to 75% was 3+, and >76% was 4+. RESULTS: Thirty-six cases were reviewed. Sixty-seven percent (24/36) of melanomas were PRAME positive (4+) while no (0/36) nevi showed 4+ positivity. Eighty-one percent (29/36) of nevi were completely PRAME negative compared to 17% (6/36) of melanomas. In 67% of cases (24/36) PRAME differentiated between benign and malignant melanocyte populations. CONCLUSIONS: We identified a high rate (67%) of differential PRAME staining in adjacent benign and malignant melanocyte populations in NAM. In PRAME positive (4+) melanomas, PRAME differentiates 100% (24/24) of benign and malignant melanocyte populations. When 4+ staining is used as the threshold for positivity, PRAME staining has a sensitivity of 67% (24/36) and a specificity of 100% (36/36). These results support PRAME IHC can assist in distinguishing melanocyte populations in melanoma arising within nevi.