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Objective: To investigate the clinicopathological, immunohistochemical and molecular characteristics of cutaneous ALK-rearranged Spitz melanocytoma. Methods: Two cases of cutaneous ALK-rearranged Spitz melanocytoma from outside hospital consultations in Department of Pathology, Affiliated Cancer Hospital of Fudan University in August 2020 and in Shanghai Ackermann Medical Laboratory in June 2022 were collected. The clinicopathological features, immunophenotypes and molecular profiles of two patients with cutaneous Spitzoid melanocytic tumor harboring ALK-rearrangement were analyzed. The literatures were reviewed. Results: The study included an 8-year-old boy and an 11-year-old girl, who presented with a polypoid lesion in the skin of right thigh and left auricle measuring 1.0 cm and 1.2 cm, respectively. Histologically, they were composed of medium to large-sized epithelioid to plump spindle cells, arranged in nested, plexiform or fascicular patterns in the superficial dermis. The neoplastic cells had abundant eosinophilic cytoplasm with round to ovoid vesicular nuclei containing prominent eosinophilic nucleoli. One case showed mild to moderate nuclear pleomorphism and mitotic activity (average, 2/mm 2 ). Immunohistochemically, the epithelioid and plump spindle cells showed diffuse and strong staining of S-100 protein, SOX10, and ALK (D5F3 and 1A4), but did not express HMB45, PNL2 and MiTF. ALK-rearrangement was detected by fuorescence in situ hybridization in both cases. Subsequent next generation sequence (NGS) analysis identified KANK1::ALK and TPM3:ALK fusions. At 34 and 14 months after surgical resection, both patients remained well with no signs of recurrence or metastasis. Conclusions: ALK-rearranged Spitz melanocytoma represents a morphologically and genetically distinct subset of Spitz melanocytoma, characterized clinically by predilection in children and adolescents, with Spitzoid morphology in plexiform pattern, positive immunohistochemical stains, and rearrangement of ALK. As some cases show atypical features and high mitotic activity, a distinction from Spitz melanoma is warranted.

Objective: To study the clinicopathologic features, diagnosis and differential diagnosis of extramedullary infiltration of acute monocytic leukemia/monoblastic sarcoma., Methods: Five cases of extramedullary infiltration of acute monocytic leukemia/monoblastic sarcoma were selected from 102 cases of myeloid sarcoma diagnosed during the period from 1990 to 2006. The clinicopathologic findings and followup data were retrospectively analyzed. Immunohistochemical study was also carried out with SP method., Results: Among the 5 cases studied, 3 were males and 2 were females, including 2 children and 3 adults. Generalized lymphadenopathy was found in 4 patients and skin lesions were observed in 2 patients. The tumor cells in all cases were positive for CD68 (KP1), CD68 (PGM1), lysozyme and CD45. They were negative for MPO, CD15, CD163, TdT, CD117, T and B cell markers. The Ki-67 index ranged from 40% to 80%. Follow-up data were available in all the 5 patients. Four of the 5 patients died of the disease, with the average survival time being 6.25 months., Conclusions: Monoblastic sarcoma is a rare disease with poor prognosis. It is almost impossible to distinguish monoblastic sarcoma from granulocytic sarcoma and other types of small round cell tumors on the basis of morphologic examination alone. Immunohistochemistry is mandatory for a correct diagnosis.

Objective: To describe the clinicopathologic features and immunophenotypes of carcinoid tumorlets in the lung with bronchiectasis, and to study the morphogenesis of these tiny tumors., Methods: The histopathologic characteristics of 3 bronchiectasis cases with carcinoid tumorlets, 11 bronchiectasis and 2 normal lungs were studied. Specific markers of the tiny tumors and the number of neuroendocrine cells (NECs) in the airway mucosa were immunohistochemically detected by EnVision method., Results: The tumorlets in the lungs presented as multi-focal nodules and most were displayed only under microscopy. These cells were arranged in clusters and foci of fascicles which were situated in the surrounding bronchial wall and bronchioles adjacent to bronchiectatic lesion, or in the scar tissues. The tiny tumors were consisted of short fusiform cells and small ovoid cells. Their nuclei were circular, oval or long fusiform and the cells were strongly argyrophilic on Grimelius staining. Intensive positive immunostaining for calcitonin, chromogranin A, NSE and gastrin were detected. Weak positive for CK, EMA, S-100 and focal positive for HC, ACTH, 5-HT were also observed. Proliferative NECs in airway mucosa adjacent to the tiny tumors increased significantly in number, compared with those in the airway mucosa of bronchiectasis without tumorlets and normal lungs (P < 0.001, respectively)., Conclusions: The clinicopathologic features and immunophenotypes of carcinoid tumorlets resemble carcinoid tumors. They are the early stage of carcinoid development. Their development may be related to the chronic pulmonary damage resulting in hypoxia and stimulating the proliferation of NECs. These pulmonary carcinoid tumorlets can be used as a model to study the tumorigenesis of carcinoid carcinoma of the lung.