Blastic plasmacytoid dendritic cell neoplasm is a rare, aggressive hematologic malignancy that commonly involves the skin and can rapidly disseminate. We report the case of a 58-year-old man presenting with a rapidly enlarging reddish nodule over the right scapular region, which grew from 9 to 20cm within 1month. Chest magnetic resonance imaging revealed marked dermal thickening with a band-like low signal on T2-weighted images ("T2-dark band"). The T2-dark dermal layer was interposed between the tumor exhibiting restricted diffusion-superficial components bulging outward and invasive subcutaneous components (the "Hamburger Sign"). 18F-FDG PET/CT demonstrated intense uptake (SUVmax, 17) in the cutaneous lesion and revealed the involvement of multiple skeletal sites. Histopathology revealed diffuse infiltration of atypical cells extending from the dermis into the subcutis. Immunohistochemistry was positive for TCF4, CD123, and TCL1, confirming the diagnosis. Radiologic-pathologic correlation suggested that the T2-dark dermal band reflects interstitial tumor infiltration that splays and preserves dermal collagen bundles, providing a basis for the T2 shortening in a collagen-rich, low-free-water layer. We propose the "Hamburger Sign" to describe characteristic imaging findings of the blastic plasmacytoid dendritic cell neoplasm, that is, the dermal T2-dark "patty" is sandwiched by tumor "buns" and the superficial and deep tumor components. Early recognition of this sign may prompt appropriate immunohistochemical work-up (plasmacytoid dendritic markers of TCF4, CD123, and TCL1) and expedite diagnosis, particularly when initial biopsy suggests undifferentiated carcinoma.

Leprosy is a chronic disease caused by Mycobacterium leprae, primarily affecting skin and nerves. Over time the progression of leprosy may be disrupted by acute inflammatory episodes known as lepra reactions. Type 2 leprosy reactions also known as erythema nodosum leprosum (ENL), are characterized by painful red nodules on the skin, along with symptoms like fever, joint pain, malaise, and systemic complications. There have been reports of unusual clinical presentations of this condition such as bullous, pustular, ulceration, erythema multiforme‑like reaction, livedo reticularis, and Sweet’s syndrome (SS)‑like presentation. The pathogenesis of sweet’s-like ENL is still uncertain. It is believed that in SS a complex interaction of various cytokines leading to buildup of pro-inflammatory cytokines in the target tissues, which trggers an abnormal immune response to certain antigens. These findings may help explain the occurrence of such unusual lepra reactions. In this case, we describe an uncommon instance of type 2 lepra reaction in a 28-year-old man who had no prior diagnosis of leprosy. The condition presented similarly to SS‑like reaction and was diagnosed by slit skin smear and histopathological examination.

In their manuscript, Dermoscopy in Merkel cell carcinoma (MCC)—A Multicenter Retrospective Study of the International Dermoscopy Society (IDS) [1], the authors have taken on a very challenging task: attempting to define the dermatoscopic features of an extremely rare, non-pigmented, highly malignant tumor. To maximize the number of cases, the authors have harnessed the worldwide membership of the IDS, a group with more than 7500 current members. These members have submitted images of 134 cases of MCC, as well as 268 control lesions. MCC is very rare. For context, in a 2021 study of all melanomas diagnosed by 27 Australasian general practitioners in 2013 [2], unpublished data reveal that there were, in addition to the 637 melanomas, only two cases of MCC, one of which was prospectively diagnosed correctly, the other having a provisional diagnosis of squamous cell carcinoma (SCC). Surprisingly, the same unpublished data from that study show that there were no other provisional diagnoses of MCC, suggesting that in 2013, it was not high on the list of considerations for pink/red, raised tumors among those GPs. In the almost four decades since dermatoscopy has become readily available, the dermatoscopic features of many diagnostic entities have been characterized. Pigmented skin lesions exhibit numerous highly specific clues, and many non-pigmented clues, such as white circles and white structureless areas in SCC [3] and stromal and vessel clues in basal cell carcinoma (BCC) [3], have been defined. Amelanotic melanomas are more challenging, leading to frequent delayed diagnosis [4], but relevant dermatoscopic clues have been characterized, including polymorphous vessels with patterns of both linear-irregular and dot vessels [3]. While polarizing-specific white lines can often help distinguish malignant from benign non-pigmented lesions, they do not distinguish melanoma from BCC [3]. The authors of the IDS study [1] have attempted to identify specific dermatoscopic clues for MCC, as exist for most common skin lesions, both benign and malignant. The study is well designed. It is much larger than any previous study on MCC, and it is the first that includes an analysis of control lesions, with these cases being submitted by contributors of cases of MCC, having been selected on the basis of appropriate pre-defined characteristics. These control lesions comprised 49 distinct diagnoses. The rating process was rigorous, without time constraints, and the statistical analysis was robust. The findings of the study are therefore valid, but—perhaps unsurprisingly given “the nature of the beast”—disappointing. Non-pigmented malignant nodules have relatively few features on which to base a diagnosis, and these features frequently overlap. The positive predictors of MCC, pink color and scales, will do nothing to help the clinician distinguish this lesion that they may encounter once or twice in a lifetime from many thousands of other non-pigmented lesions they will assess. No discriminatory features were identified with respect to vessel patterns or shiny white structures. The concluding statement that amelanotic melanoma should be included in the differential whenever MCC is suspected is very telling. Nothing identified in this study discriminates between those entities. Before we published the first dermatoscopic image of a MCC in 2009 [5], its dermatoscopic features were unknown (Figure 1). That has changed, however; in spite of a large, well-designed and well-executed study, there do not appear to be even reasonably specific dermatoscopic clues to a diagnosis of MCC. Neither are there specific dermatoscopic features to discriminate MCC from other raised, non-pigmented lesions. For the time being, the clinical features of an abruptly appearing, rapidly growing, pink or red nodule (Figure 1) may continue to trump dermatoscopic features when those features lack specific clues to another diagnosis. Open access publishing facilitated by The University of Queensland, as part of the Wiley - The University of Queensland agreement via the Council of Australian University Librarians. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.

Reevaluating red nodules in hidradenitis suppurativa: clinical, dermatoscopic and histopathologic correlation.

Atypical fibroxanthoma (AFX) is an uncommon dermal neoplasm that predominantly affects sun-exposed head and neck skin in older adults. It is locally aggressive and can resemble other cutaneous malignancies, requiring histopathologic and immunohistochemical confirmation and careful surgical management, with Mohs micrographic surgery reducing recurrence compared with wide local excision. An 81-year-old woman presented with an elevated skin lesion on the right side of her face in the eyebrow arch. The lesion presented as a peanut-sized red nodule that grew over a 6-month period with breakthrough bleeding and crusting. The excised specimen was ultimately diagnosed as atypical fibroxanthoma. This study reports a rare case of atypical fibroxanthoma of the face in a female. This case expands the clinicopathologic spectrum of atypical fibroxanthoma by documenting a rare lesion of the eyebrow arch in an elderly woman, underscores the importance of rigorous histopathologic and immunohistochemical assessment to secure the diagnosis and exclude mimics, and shows that complete surgical excision can achieve short‑term remission; continued surveillance is warranted given the risk of local recurrence, and further reports are needed to refine site‑specific management and outcomes.

Juvenile xanthogranuloma is a rare but common form of non-Langerhans cell histiocytosis that affects infants under 2 years of age. In most children, the disease is limited to the skin, manifested by red or yellow nodules 0.5–1.0 cm in diameter, single or multiple, arising on the scalp, face, neck, and trunk. Elements may spontaneously disappear within several months or several years. Most patients with cutaneous juvenile xanthogranuloma do not require treatment. Systemic involvement is observed in patients with multiple cutaneous nodules and can be accompanied by life-threatening symptoms with a mortality rate of about 4% and rarely resolves spontaneously. The article presents a clinical observation of an atypical course of systemic juvenile xanthogranuloma with involvement of the central nervous system, skin, lungs, liver, bladder, uterus, and vagina. The clinical and histological features of the disease are characterized, and various approaches to targeted therapy with BRAF and MEK inhibitors are shown.

Background: Kaposi sarcoma (KS) is an HIV‑defining vascular tumor that may initially present in the oral cavity and mimic other vascular lesions, making biopsy essential for diagnosis. Case presentation: A 47-year-old man presented with a 1-month history of a progressively enlarging red nodule on the right buccal mucosa. Clinical examination revealed multiple painless angiomatous papules on the right vestibule. One month later, lesions had spread, becoming diffuse bluish-violaceous nodules on the oral mucosa, associated with cervical and inguinal lymphadenopathy, violaceous skin plaques on the limbs and trunk, and chronic diarrhea. Oral biopsy suggested vascular proliferation, while skin biopsy confirmed Kaposi sarcoma. HIV serology was positive, establishing HIV-associated KS. Combination antiretroviral therapy was initiated, with additional local or systemic treatment considered according to disease burden Discussion: Oral KS can progress from flat, asymptomatic red‑to‑purple lesions to papules and nodules that may ulcerate or bleed and impair oral function; the palate, gingiva, and tongue are commonly affected, with buccal mucosa and vestibule involvement less frequent but observed in this case. Differential diagnoses include bacillary angiomatosis, hemangioma, pyogenic granuloma, inflammatory or drug‑induced gingival enlargement, melanoma, lymphoma, and leukemia. Conclusion: Early recognition of atypical oral vascular lesions can expedite HIV testing and treatment initiation in HIV‑associated KS.

Merkel's carcinoma is a rare but highly aggressive cutaneous neuroendocrine tumor whose incidence has increased due to an aging population and increased UV exposure. It is characterized by rapid growth, high risk of recurrence and early metastatic spread. Two subtypes have been identified: Merkel polyomavirus-related (MCPyV), present in 80% of cases in Europe, and UV-related. The main risk factors are advanced age, male gender, light phototypes and immunosuppression. Clinically, it appears as a painless, red or purplish nodule, often on photo-exposed areas. Diagnosis is based on histopathology and immunohistochemistry (CK20+ and synaptophysin+). Extension assessment is essential, and relies on PET-CT, brain MRI and lymph node ultrasound. Staging follows the AJCC 8th edition, distinguishing between localized (I/II), lymph node involved (III) and metastatic (IV) stages. Treatment is based on surgery (excision with 1cm margins) and adjuvant radiotherapy. In the case of lymph node involvement, lymph node dissection and radiotherapy are recommended. Metastatic forms now benefit from immunotherapy (anti-PD-1/PD-L1), which has improved prognosis. Merkel carcinoma has a high recurrence rate (25-50%). Monitoring is based on regular clinical and radiological follow-up over several years. Biomarkers such as NSE and anti-MCPyV serology are currently being evaluated.

Backgroud: Merkel cell carcinoma is a cutaneous tumor, also known as neuroendocrine carcinoma, that is infrequent and highly aggressive, with a high mortality rate. 1 It primarily affects individuals over 60 years of age, those with immunosuppression, or those infected with the polyomavirus (MCPyV). It is an underdiagnosed tumor due to the nonspecificity of its clinical and dermatological manifestations. The definitive diagnosis is made by histopathological study, with identification of the sentinel lymph node being essential, since the presence of metastases is associated with a significant decrease in five-year survival. Although there is no optimal treatment, surgery remains a therapeutic pillar, complemented by radiotherapy and immunotherapy as adjuvant treatments. Material And Methods: The study was conducted using a mixed-method design, comprising a descriptive literature review conducted in scientific databases (PubMed, SciELO, Cochrane Library, and Elsevier), prioritizing recent population-based studies addressing the incidence, mortality, and survival associated with Merkel cell carcinoma. This was complemented by clinical follow-up of a 55-year-old female patient diagnosed with the condition in 2021. Results: The patient consulted on 06/25/2021 for a painless red nodule in an exposed region. The diagnosis was confirmed by biopsy on 01/07/2021. Despite the treatment, he developed lymph node and distant metastases and died in 2023. The revised bibliography shows a low overall survival, especially in advanced stages. Conclusion: The CCM continues to be an underdiagnosed neoplasm. Its early detection is key to improving prognosis and increasing survival. Despite the early diagnosis, the patient did not exceed three years of survival, which shows that the CCM can have aggressive clinical behavior even in the initial stages.

Hemangiosarcoma is a malignant neoplasm of vascular endothelial cell origin that is rare in nonhuman primates (NHPs) and humans. This report describes the clinical, gross, and histopathologic findings of metastatic hemangiosarcoma in a rhesus macaque. A 4.8-year-old female Indian-origin rhesus macaque presented to the Tulane National Biomedical Research Center clinic with right hindlimb lameness and poor body condition. On physical examination, there was significant muscle atrophy of the right leg and pelvis. Radiographs revealed severe bone degeneration and lysis of the right tibia with pulmonary nodules. On necropsy, the right tibia was markedly thickened at least two times the normal size. Multifocal, 1- to 7-mm-diameter dark red nodules were present in the periosteum, compact cortical bone, and medullary cavity. Multifocal dark red nodules measuring 1-10 mm were present in the liver and lung. Histologically, the nodules were composed of neoplastic endothelial cells forming irregular vascular clefts and anastomosing vascular channels. Neoplastic cells often wrapped collagenous stroma. Neoplastic cells stained positive with CD31, as well as with von Willebrand factor immunohistochemical stains. Hemangiosarcoma in NHPs is exceptionally rare. To our knowledge, this represents the first case of metastatic hemangiosarcoma originating in bone in an NHP.

Neoplasms with splenic involvement in dogs at necropsy: Macroscopic presentation patterns in 262 cases.

Amirthalingamia macracantha (Joyeux and Baer, 1935) larvae, a member of the Gryporhynchidae family (Cestoda: Cyclophyllidea), are commonly found in a variety of African fish species, including Nile tilapia (Oreochromis niloticus, Linnaeus, 1758). Nonetheless, little is known regarding their existence in native Egyptian fish species. Two hundred O. niloticus were examined in the current investigation, using standard parasitological techniques to detect the presence of these larvae in different fish organs. According to this study's findings, A. macracantha larvae were found in 35% of the microscopically examined samples as red nodules, attaching to the serosa of both the anterior and posterior sections of the intestine and stomach, respectively. The mean abundance of the infection was 3.5 ± 0.05 (CI 95% 3.4-3.5), and its mean intensity was 10 ± 1.7 (CI 95% 8.2-11.7). The existence of two rows of twenty rostellar hooks of varying lengths is the main characteristic of the parasite. The upper row consisted of four large hooks and six smaller ones, while the lower row contained smaller hooks of consistent length. According to histopathological analysis, the larvae with a hook-and-spiny rostellum were affixed to the stomach serosa of O. niloticus. Additionally, there was a notable presence of degranulated mast cells and lymphocytes of varying sizes within the stomach's lamina propria, submucosa, and blood vessels, as well as a loss of gastric epithelium, fibrosis, and enlargement of submucosal lymph vessels. This study offers a succinct description of this larval stage, representing the first reported occurrence of its presence in Egyptian O. niloticus.

Soybean serves as a crucial source of plant-based protein for human diets. Recently, there is a growing incentive to extend the range of this crop to more northern latitudes, in order to enable profitable soybean production in Europe. To reach economic yields, soybean requires inoculation with symbiotic, diazotrophic rhizobial bacteria. However, the performance of commercial inocula is often variable under local conditions. Here, we present the citizen science project "Soy in 1,000 Gardens", a large-scale trapping experiment for isolating local soybean-nodulating rhizobia in Flanders, Belgium. We identified two locally isolated Bradyrhizobium strains performing at least as well as commercial strain B. diazoefficiens G49 in local field trials. Additionally, we found that nutrient content, microbial alpha diversity, and the presence of arbuscular mycorrhizal fungi in the soil were correlated with nodulation. Finally, we report a correlation between low bacterial alpha diversity and red nodule interior, and identified Tardiphaga as a dominant colonizer of red nodules.

Clinical Pathologic Conference Case 1: A reddish nodule on the midline hard palate

Reddish Nodule on the Left Shoulder.

A 44-year-old man presented with multiple occasionally itchy and bleeding nodules on the scalp for 6 months. Cutaneous examination revealed multiple solitary and grouped dull red nodules of size ranging from 2 × 2 cm to 4 × 3.5 cm on the scalp, predominantly in the occipital region. There were no enlarged lymph nodes.

Abstract Merkel cell carcinoma (MCC) is a rare, aggressive nonmel­anoma skin cancer with high metastatic potential and a 33% mortality rate, higher than that of melanoma (Eng TY, Boersma MG, Fuller CD et al. Treatment of Merkel cell carcinoma. Am J Clin Oncol 1997; 20: 184–8). Avelumab, an anti-programmed death ligand 1 immune checkpoint inhibitor, has demonstrated durable responses and improved survival in MCC compared with chemotherapy. While generally well tolerated, it can cause immune-related adverse events (Kaufman HL, Russell J, Hamid O et al. Avelumab in patients with chemotherapy-refractory metastatic Merkel cell carcinoma: a multicentre, single-group, open-label, phase 2 trial. Lancet Oncol 2016; 17: 1374–85). We present the first reported case of newly diagnosed sarcoidosis in a patient receiving avelumab for metastatic MCC. A 69-year-old man had membranous glomerulonephritis treated with tacrolimus. He presented with a tender red dermal nodule on the left shin, surrounded by smaller similar lesions. He had multiple palpable lymph nodes. Computed tomography (CT) of the whole body confirmed left aortic, iliac chain and inguinal adenopathy. Biopsy of a left-leg lesion and lymph nodes later confirmed MCC. Following multidisciplinary team discussion, tacrolimus was stopped, and he commenced palliative avelumab for metastatic MCC. After 9 months of avelumab the leg lesions had healed completely. No new MCC lesions or metastases were identified. His renal function and electrolytes were stable. One year into treatment, he developed multiple erythematous papules on his upper chest. Biopsy reported non-necrotizing granulomatous inflammation, in keeping with cutaneous sarcoid. Positron emission tomography (PET)-CT demonstrated bilateral hilar and mediastinal nodal activity. He also had elevated calcium levels of 3.02 mmol L−1. Given these findings, he was diagnosed with sarcoidosis secondary to avelumab. Oral corticosteroids caused the sarcoid lesions to regress and normalized serum calcium levels. Follow-up PET-CT showed thoracic nodal avidity regression. Avelumab was paused for 3 months, then restarted. However, after 1 month, hypercalcaemia and deteriorating kidney function recurred. Avelumab was permanently discontinued on completion of the planned 2-year course of treatment. Immunotherapy-induced sarcoidosis is a rare but recognized immune-related adverse event. We believe this to be the first reported de novo case secondary to avelumab and we could find only a single report of known sarcoidosis reactivation in the literature (Tun Min S, Nordman IIC, Tran HA. Hypercalcaemia due to sarcoidosis reactivation in patient with metastatic Merkel cell carcinoma treated with avelumab. Case Rep Oncol 2019; 12: 621–7). Given the ever-increasing role of immunotherapy to treat advanced skin cancers, clinicians need to be aware of these complications as the incidence is likely to increase.

Red nodule on the scrotum.

NUM can resemble nodular melanomas, appearing suddenly as an ulcerated nodule that grows quickly.2 NUM is usually misdiagnosed and notoriously mimics other tumors (such as periungual pyogenic granuloma in our case). Herein we are presenting a rare case of nail unit melanoma in a 52-year-old female who presented with insidious onset, slowly progressive soft to firm, non-tender, red nodule with a proximal nail fold showing bluish-black pigmentation over the left thumb area associated with bleeding since 1 year. Histopathology and immunohistochemistry are suggestive of melanoma. Surgical oncology reference was sought and digital amputation was considered.

Red nodule on the face of a middle-aged woman.