Merkel cell carcinoma in situ (MCCIS), especially when unaccompanied by invasive Merkel cell carcinoma, is exceptionally rare. Most reported cases of MCCIS without invasion demonstrate the typical immunophenotype of invasive MCC, including cytokeratin 20 (CK20) positivity and thyroid transcription factor-1 (TTF-1) negativity. Here we report a case of MCCIS without invasion exhibiting a phenotype not previously reported in MCCIS: CK20 negativity with diffuse nuclear TTF-1 positivity. Arising within a seborrheic (stucco) keratosis in a 78-year-old woman, the lesion demonstrated an entirely intraepidermal proliferation of atypical cells with neuroendocrine differentiation by histology (high nuclear-to-cytoplasmic ratio, crush artifact, and nuclear molding) and immunohistochemistry (positive synaptophysin, chromogranin, neuron-specific enolase, INSM1, and SATB2). The lesion was negative for squamous markers (cytokeratin 903, cytokeratin 5/6, p40, and p63), Merkel cell polyomavirus (MCPyV/CM2B4), and neurofilament. A review of the literature identified no prior TTF-1-positive MCCIS. To our knowledge, the present case represents the first reported TTF-1-positive MCCIS and only the second reported CK20-negative MCCIS. This unusual phenotype expands the recognized immunophenotypic spectrum of MCCIS and highlights a potential diagnostic pitfall.

Cutaneous melanoma is an aggressive malignancy whose early detection is crucial for prognosis; however, some lesions can mimic nonmelanocytic conditions, leading to diagnostic errors. This retrospective study evaluated the frequency and characteristics of melanomas initially misclassified as nonmelanocytic lesions. All excised cutaneous lesions at the Dermatology Unit of the University Hospital Federico II of Naples between January 2021 and December 2024 were analyzed. Among 1500 histologically confirmed melanomas, 70 cases (4.7%) were initially diagnosed as nonmelanocytic based on clinical and dermoscopic evaluation. The most frequent misdiagnoses were basal cell carcinoma (40%), seborrheic keratosis (14.3%), and squamous cell carcinoma (8.6%). Other less common misclassifications included dermatofibroma, actinic keratosis, and vascular or adnexal lesions. The proportion and distribution of these cases remained stable over time, with no statistically significant differences across the study period. Amelanotic and hypomelanotic melanomas were particularly prone to misinterpretation due to the absence of typical pigmentation, often resembling inflammatory, vascular, or keratinizing lesions. These findings highlight the significant clinical heterogeneity of melanoma and the limitations of dermoscopy in atypical presentations. An integrated diagnostic approach combining clinical evaluation, dermoscopic assessment, patient risk factors, and a low threshold for histopathological examination remains essential. Increased awareness of melanoma simulators is crucial to reduce diagnostic delays and improve patient outcomes.

We report a case of clonal seborrheic keratosis (CPSK) adjacent to Bowen's disease (BD) in a 29‑year‑old male with no history of chronic sun exposure. The lesion presented as a brown, flat papule on the right side of the back. Histopathologically, the CPSK component featured well‑demarcated intraepidermal nests of basaloid keratinocytes, consistent with the Borst‑Jadassohn phenomenon. Adjacent areas showed full‑thickness epidermal atypia, nuclear pleomorphism, and numerous mitotic figures, including atypical forms, characteristic of BD. No clear transitional zone was identified between the two components. These findings align most closely with a collision tumor-coincidental coexistence of two independent neoplasms-rather than true malignant transformation of CPSK into BD. This case underscores the need for careful histologic evaluation to distinguish collision from transformation, particularly in the absence of chronic ultraviolet exposure.

Seborrheic keratosis is a common benign skin tumor that affects most individuals, particularly later in life. Despite its high prevalence, the underlying biology of seborrheic keratosis remains poorly understood. In this study, we performed whole-exome sequencing and spatial transcriptomics on a cohort of seborrheic keratosis and solar lentigo lesions to gain insight into their molecular landscape. Our results reveal a high mutational burden driven by solar UV damage, with recurrent somatic variants observed in genes such as FGFR3, NOTCH1, and TP53. Spatial transcriptomic analysis uncovered a complex tissue architecture with significant heterogeneity across lesion subtypes. Furthermore, differential gene expression analysis highlighted the dysregulation of the Wnt signaling pathway as a key feature in the pathogenesis of these lesions. Together, our findings provide insights into the molecular mechanisms driving seborrheic keratosis and solar lentigo, with implications for understanding their development and progression.

Given clear cell acanthoma's overlapping similarities with psoriasis, we compared the presence of psoriasis and its known cardiovascular comorbidities in patients with clear cell acanthoma with patients with a control benign skin lesion (seborrheic keratosis). We found no significant relationship between clear cell acanthoma and psoriasis.

Background/Objectives: The early identification of skin cancer by standard RGB dermoscopy is a clinical difficulty because of the complex visual differences between impacted lesions and healthy tissue. Methods: For the biomedical challenge, a novel approach to signal processing and image reconstruction is introduced in this study, called the spectrum-aided visual enhancer (SAVE). The proposed SAVE mechanism aims at reconstructing the diagnostically relevant spectral information from the conventional RGB dermoscopic images using the principles of hyperspectral imaging (HSI) and band selection (BS). After quality control and pre-processing, the images in the ISIC2019 dataset were selected, with 865 images that contain basal cell carcinoma (BCC), seborrheic keratosis (SK), and actinic keratosis (AK) lesions. To reduce data leakage, the dataset was split into training, validation, and testing subsets of 70%, 20%, and 10%, respectively. Five supervised deep learning object detection models were trained and tested on the conventional RGB image dataset and on the SAVE-enhanced dataset. Five supervised deep learning object detection models, namely, YOLOv8, YOLOv10, YOLOv11, SSDLite, and SSD, were trained and tested on the conventional RGB image dataset and the SAVE-enhanced dataset. Additional repeated experimental assessments and statistical comparisons were also carried out to evaluate the improvement in performance. Results: The experimental results showed that the SAVE-based pre-processing always yielded better performance in terms of lesion detection than conventional RGB image processing. The SAVE framework for SSD was evaluated and compared with all other evaluated models and was found to be the most successful, with an accuracy of 96%, a precision of 97%, a recall of 96%, and an F1 score of 96%. Conclusions: The results indicate that the proposed SAVE framework could be a promising RGB-compatible spectral enhancement technique for boosting skin cancer detection and computer-aided dermatologic analysis with the aid of AI.

Pediatric dermatoses presenting as follicular papules are common entities encountered in clinical practice. These are a heterogeneous group of disorders of infectious or noninfectious origin that commonly present as regularly spaced, small papules with or without perifollicular inflammation. Inflammatory causes include follicular eczema, pityriasis rubra pilaris, lichen nitidus, follicular seborrheic dermatitis, keratosis pilaris and its variants, keratosis circumscripta, follicular psoriasis, lichen spinulosus, follicular lichen planus, follicular mucinosis, perforating folliculitis, follicular porokeratosis, and follicular dermographism. These conditions may arise due to filaggrin mutations, keratinization defects, autoimmunity, or microbial triggers. Nutritional causes include phrynoderma and scurvy, while connective tissue diseases such as dermatomyositis and chronic cutaneous lupus erythematosus are autoimmune. Additional categories include infectious, genetic, hormonal, environmental, frictional, malignant, nevus-related, iatrogenic, and idiopathic entities. An early and accurate diagnosis is essential for proper management and reducing disease-associated apprehension in children and/or their parents. This review attempts to describe the role of history taking and clinical examination, including morphology, location, pattern of distribution, and associated features, while dealing with a child with follicular-based papules. In addition, it delineates the role of dermoscopy and pathological examination in reaching a correct diagnosis. Furthermore, it describes the available treatment options and disease course of various follicle-based dermatoses.

In recent years, dermatoscopy has emerged as a valuable adjunctive tool for the diagnosis of various cutaneous disorders. Initially developed for the evaluation of melanocytic lesions, this non-invasive technique has since demonstrated significant utility in the assessment of non-melanocytic hyperpigmented dermatoses. This review provides an up-to-date and practical overview of the dermatoscopic manifestations of common non-melanocytic hyperpigmented conditions, including melasma, nevus of Ota, freckles, lentigines, solar lentigines, seborrheic keratosis, porokeratosis, acquired dermal macular hyperpigmentation, lichen planus-like keratosis, pigmented actinic keratosis, pigmented Bowen's disease, basal cell carcinoma, and acanthosis nigricans. Many of these hyperpigmented disorders exhibit distinct and characteristic dermatoscopic features. Given the clinical diagnostic challenges posed by these conditions and their significant psychological impact on patients, dermatoscopy offers a complementary approach to enhance the accuracy of evaluation and differential diagnosis.

We present the case of a 54-year-old woman with a clinically suspected malignant melanoma. Histology, however, revealed the unexpected diagnosis of large cell acanthoma. This is a benign epidermal neoplasm that is poorly understood and underreported in the literature. The clinical and dermoscopic appearance in our patient differs from previously reported cases. We draw attention to this heterogeneous lesion and encourage further investigation into its classification and distinguishing features, which may ultimately inform optimal management for patients.