SMARCB1 (INI1) is one of the switch/sucrose nonfermentable (SWI/SNF) complexes whose loss is associated with several tumors. SMARCB1 (INI1)‐deficient intrathoracic neoplasms are extremely rare and known to be highly malignant and lethal. This report presents the case of a patient diagnosed with SMARCB1 (INI1)‐deficient intrathoracic neoplasm during chemotherapy for plasma cell myeloma. A 77‐year‐old male patient complained of cough, bloody sputum, and fever with an enlarged right lung mass and pleural effusion. His cytological examination revealed undifferentiated epithelioid and rhabdoid/plasmacytoid cells with bi‐ or multinucleation, vacuolization, mitosis, and pleomorphism. However, it was difficult to distinguish the relapse of plasma cell myeloma as atypical plasmacytoid cells were detected. Immunohistochemically, the neoplastic cells showed a loss of SMARCB1 (INI1) expression in the cell block of pleural fluid and in the right lung of the autopsy specimen. Further, the patient was diagnosed with SMARCB1 (INI1)‐deficient intrathoracic neoplasm of the right lung based on histological and autopsy findings. To the best of our knowledge, this is the first report of cytomorphology in a SMARCB1 (INI1)‐deficient intrathoracic neoplasm.

Anaplastic lymphoma kinase-positive anaplastic large cell lymphoma (ALK+ ALCL) is characterised by large lymphocyte-like cells with abundant cytoplasm and variable-shaped nuclei, often resembling horseshoes or kidneys. These cells have a specific genetic translocation involving the ALK gene and are positive for ALK and CD30 by immunohistochemistry. 1 In children, ALK+ ALCL is the most common subtype of T-cell lymphoma, accounting for 10%-30% of lymphomas. ALK+ ALCL exhibits a wide range of morphological patterns, with the common variant comprising 60% of cases, followed by lymphohistiocytic (10%), small-cell (5%-10%), and Hodgkin-like (3%) variants. 2 In small cell variant ALCL (SC-ALCL), large hallmark cells are few with the preponderance being small-to medium-sized tumour cells.Tumour cells in peripheral blood indicate the leukaemic phase, which is associated with poor prognosis. Among the morphological variants, patients with SC-ALCL often show the leukaemic phase, thus accurate and prompt diagnosis is essential for effective treatment. 3 How to cite this article: Shimaguchi C, Mizuguchi K, Fujita K, Shimoda T, Ikeda H. Cytological examination of peripheral blood cell block to diagnose small cell variant ALK-positive anaplastic large cell lymphoma.

BackgroundNephroblastoma (NB) is a malignant embryonal neoplasm derived from nephrogenic blastemal cells. NB usually forms a solid mass, but in extremely rare cases, it may show cystic changes.Case presentationA six-month-old girl with persistent high fevers was found to have pyuria and bacteriuria. Ultrasonography revealed multilocular cysts in the right kidney. Right nephrectomy was performed with cyst wall rupture during surgery. An intraoperative rapid diagnosis, based on peritoneal fluid cytology, confirmed three components of blastemal, stromal, and epithelial cells. The blastemal cells were dyshesive, with scant to no cytoplasm and were the predominant cell type. The spindle-shaped stromal cells were arranged in fascicles. The epithelial cells demonstrated tubular structures. Macroscopically, the resected cystic tumor measured 80 mm in maximum diameter with a prominently thin cyst wall, but solid areas were also apparent. Histologically, the tumor was diagnosed as cystic NB (blastemal-predominant) displaying a triphasic pattern. Hyperchromatic nuclei and apoptotic bodies were found. The clinical stage classification of Japan Wilms Tumor Study group was 3. The patient was treated with chemotherapy and radiotherapy. Tumor recurrence and metastasis have not been observed in the 8 months since surgery.ConclusionThis is an extremely rare case of infantile cystic NB. We diagnosed the NB cells that appeared in the peritoneal fluid by intraoperative rapid cytology. Cytological examination proved to be a very useful technique for determining the clinical stage of NB. Additionally, we propose that massive tumor degeneration and necrosis be considered as a pathogenic mechanism of cyst formation in NB.