Objective: To investigate the clinicopathological features, immunophenotype and molecule characteristics of EWSR1::CREM fusion malignant epithelioid neoplasm in soft tissue. Methods: The clinical and pathological data of 2 cases of EWSR1::CREM fusion malignant epithelioid neoplasm in soft tissue diagnosed at the Department of Pathology, Beijing Jishuitan Hospital, Beijing, China from May 2023 to May 2024 were analyzed. Immunohistochemical study, fluorescence in situ hybridization (FISH) and next generation sequencing (NGS) were performed. Relevant literature was reviewed. Results: There were one male and one female patients, aged 35 and 29 years, respectively. The tumors developed in the somatic soft tissue, including calf and chest wall, and were 6.0 and 6.2 cm in size, respectively. The imaging studies suggested space-occupying lesions in muscle tissue. Case 1 did not involve the bone, while Case 2 showed fracture of the 8th rib. Microscopically, a fibrous pseudocapsule surrounded by lymphocytes and plasma cells was identified. The tumors were composed of small to medium-sized round and short spindle-shaped cells, showing nodular or sheet-like pattern. The tumor cells showed round nuclear outline, coarse chromatin with prominent nucleoli. Immunohistochemically, tumor cells showed diffuse positivity of ALK (D5F3), MUM1 and Syn, focal or patchy positivity of CKpan, EMA, S-100, NSE, WT-1 and SMA, and a high Ki-67 index (20%-30%). FISH demonstrated break-apart signals of EWSR1 gene in the 2 cases. NGS revealed EWSR1::CREM gene fusion. Case 2 showed an ATRX gene mutation. The two patients were free of recurrence or metastasis at the 10-month and 1-month follow-up, respectively. Conclusions: EWSR1::CREM fusion malignant epithelioid neoplasm is rare and lacks distinctive morphological and immunohistochemical features. FISH and NGS can help make a definitive diagnosis.

Objective: To investigate the expression of keratin 1 (KRT1) and sialyl-Tn antigen (sTn) in cervical squamous cell carcinoma and its possible mechanism. Methods: Six cervical squamous cell carcinoma specimens were collected at the First Affiliated Hospital of Soochow University, Suzhou, China from 2022 to 2023. Spatial transcriptomics analysis was performed on the paraffin sections of 6 patients to analyze the transcriptomes of invasive squamous cell carcinoma and adjacent normal cervical squamous epithelium. The differential gene KRT1 was selected. Kaplan-Meier survival analysis was used to examine the prognostic value of KRT1 in cervical squamous cell carcinoma patients using the TCGA database. The possible downstream molecule sTn was identified according to literature research. Immunohistochemistry was carried out to investigate the expression of KRT1 and sTn proteins in the primary tumor and metastases of cervical squamous cell carcinoma (40 cases with pelvic lymph node metastasis and 30 cases without). Spearman correlation analysis was conducted to analyze the correlation of their expression. Results: The spatial transcriptomic results of the 6 specimens indicated that the level of KRT1 mRNA significantly decreased in cervical squamous cell carcinoma (compared with that in adjacent normal cervical squamous epithelium), while Kaplan-Meier survival analysis revealed that cervical squamous cell carcinoma patients with low KRT1 mRNA levels (versus high) had a worse prognosis. Immunohistochemistry proved that KRT1 expression was significantly lower in cervical squamous cell carcinoma than in adjacent normal squamous epithelium (P<0.05), but sTn showed the opposite change (increased in carcinoma, P<0.05). The expression changes of KRT1 and sTn were inversely correlated (r=-0.217, P<0.05). In addition, the expression levels of KRT1 and sTn in lymph node metastases were not significantly different from those in primary tumors. Conclusions: The decreased expression of KRT1 in primary cervical squamous cell carcinoma and lymph node metastasis may promote tumor cell proliferation and inhibit apoptosis by upregulating sTn, contributing to the poor prognosis of advanced cervical squamous cell carcinoma.

Objective: To investigate clinicopathologic characteristics and molecular genetic profiles of embryonal rhabdomyosarcoma (ERMS) of the middle ear. Methods: A total of 11 cases of primary middle ear ERMS diagnosed and treated at the Fudan University Affiliated Eye and ENT Hospital between January 2016 and June 2024 were collected. Their clinicopathologic features, immunophenotypes, and molecular genetic alterations were analyzed. Relevant literature was reviewed. Results: There were 8 male and 3 female children. The mean age was 6 years, median age, 6 (5, 7) years, with a range of 1 to 11 years. Clinical manifestations included otorrhea, ear pain, ear fullness, tinnitus, and hearing loss, with some patients also presenting with facial paralysis, hoarseness, and choking on drinking. Otoscopic examination revealed granulomatous neoplasms in the external auditory canal. Imaging studies showed irregular soft-tissue masses in the middle ear region, accompanied by bony destruction and invasion of adjacent structures. Histologically, 10 of the tumors were composed of primitive small round cells, stellate cells, and short spindle-shaped cells, with an alternating loose and dense distribution pattern, and varying degrees of rhabdomyoblastic differentiation in some areas. One tumor exhibited the classic botryoid subtype morphology. Immunohistochemistry supported the diagnosis of rhabdomyosarcoma, and the Ki-67 proliferation index ranged from 40% to 80%. Next-generation sequencing (DNA-seq) was performed on 9 cases, revealing copy number variations of chromosome 7 in 4 cases, PDE4DIP mutations in 5 cases, and C19orf69::TPM3 gene fusions in 6 cases. HPV PCR testing showed HPV11 positivity in 2 cases. All 11 patients underwent surgical treatment, with 4 patients receiving adjuvant chemoradiotherapy. Follow-up until February 2025 revealed 8 deaths, among which 4 cases harbored both C19orf69::TPM3 fusions and PDE4DIP mutations and one had C19orf69::TPM3 fusions alone. Conclusions: ERMS of the middle ear is a rare type of malignant tumor with a relatively poor prognosis. Our study indicates that the concurrence of PDE4DIP mutation and C19orf69::TPM3 gene fusion may indicate poor prognosis in middle ear EMRS, providing a potential target for subsequent individualized treatment.

Objective: To investigate the clinicopathological features, immunophenotype, and gene rearrangement status of hyalinizing clear cell carcinoma (HCCC) of the salivary glands, in order to better understand this rare tumor and improve its precision diagnosis and treatment. Methods: A total of 65 cases of salivary gland HCCC diagnosed at the Peking University School and Hospital of Stomatology, Beijing, China between January 2001 and May 2024 were collected. Clinical features, pathological characteristics, EWSR1 gene rearrangement, and follow-up data were analyzed. Results: There were 33 males and 32 females. The age of the patients ranged from 22 to 85 years, with a median age of 54.0 (40.0, 63.5) years. 93.8% (61/65) of the tumors occurred in the minor salivary glands, most commonly in the palate. Microscopically, the tumors were mainly composed of clear tumor cells. Squamous differentiation was observed in 66.2% (43/65) of the tumors, and mucinous cells in 36.9% (24/65). The tumor stroma showed delicate fibrous septa or hyalinized sheets between tumor nests. Lymph node metastasis occurred in 12.3% (8/65) of the cases, and high-grade transformation was observed in 6.2% (4/65). Tumor cells were all positive for p40 and p63, while SOX10 was positive in 12.3% (8/65) of them. Myoepithelial markers were negative. EWSR1 gene rearrangement was detected in 96.6% of the tumors. Follow-up data showed a 5-year overall survival rate of 93.8%, a local recurrence rate of 9.2%, and a distant metastasis rate of 4.6%. Conclusions: HCCC predominantly arises in minor salivary glands and generally has a favorable prognosis. However, a small proportion of the cases may show high-grade transformation, lymph node metastasis, local recurrence, or distant metastasis. It thus requires long-term and regular follow-up. Accurate diagnosis should be based on a comprehensive assessment of histopathological features, immunophenotype, and gene fusion status.

Objective: To analyze the cytological, histological, immunohistochemical, and molecular pathological features of hyalinizing trabecular tumor (HTT). Methods: Clinical and pathological data of the HTT cases diagnosed at Shanghai Sixth People's Hospital affiliated to Shanghai Jiao Tong University School of Medicine between 2020 and 2024 were collected and analyzed. HE staining, special staining, immunohistochemical staining, and next-generation sequencing were performed on all cases. Results: Among the 10 HTT patients, 4 were male and 6 were female. The age at onset ranged from 29 to 85 years, with a median age of 49 (35,61) years. The maximum tumor diameter ranged from 0.3 to 5.3 cm. Cytologically, the smears were hypercellular and showed tumor cells arranged in nested clusters with visible basement membrane-like material. The nuclei were oval with finely granular chromatin, and nuclear pseudoinclusions were readily identifiable. Histologically, the tumors were well demarcated. The tumor cells were arranged in a paraganglioma-like pattern, exhibiting typical nuclear features of papillary thyroid carcinoma and psammoma bodies. Yellow bodies were observed in the cytoplasm. The stroma was rich in hyalinized material, which was periodic acid-Schiff stain (PAS)-positive. Immunohistochemically, the tumor cells showed diffuse expression of TTF-1 and focal expression of thyroglobulin. Aberrant immunoreaction with Ki-67 was present in the cytoplasm and membrane of the tumor cells. Molecular testing was performed on 8 cases. The PAX8-GLIS3 gene fusion was detected in 7 cases. Among these fusion-positive cases, 4 exhibited additional genetic abnormalities: one concurrent TSHR point mutation (p.D617H); one concurrent HRAS point mutation (p.Q61R); one concurrent LRP1B point mutation (p.S1752L), SUGCT point mutation (p.K137), and TERT point mutation (p.P785L); one concurrent MTOR mutation (7528+27A>T) and FLT3 mutation (p.E77K). The key initiating factors for thyroid carcinoma, including the BRAF V600E mutation and RET rearrangements, were absent in all cases tested. Conclusions: Cellular pleomorphism, yellow bodies and basement membrane-like material constitute important cytological and histological features for the differential diagnosis of HTT. Immunophenotypically, thyroglobulin may show focal expression, while Ki-67 is typically localized in the tumor cell membrane and cytoplasm. This study also demonstrates that PAX8-GLIS3 fusion is a characteristic molecular abnormality in HTT, although cases with wild type of GLIS gene may also present. Although rare, HTT may harbor point mutations in HRAS and TSHR, and other uncommon genetic alterations.

In recent years, with the rapid development of artificial intelligence technology, the application of deep learning in the field of pathology has been continuously expanding. Particularly, the rise of multimodal data fusion methods has opened up new technical paths for the precise diagnosis, prognosis assessment, and individualized treatment of tumors. By integrating multi-level and multi-source data such as clinical information, pathological omics, molecular omics, and imaging omics, deep learning models can identify potential associated features and key biological mechanisms that are difficult to reveal by a single modality, thereby significantly improving the accuracy of disease classification and the scientific nature of risk stratification. This article systematically reviews the research progress of multimodal data fusion methods based on deep learning in the field of pathology in recent years, focuses on sorting out different types of fusion strategies, evaluates their advantages and challenges in practical clinical applications, and looks forward to future development trends.

Medullary thyroid carcinoma (MTC) is the most common neuroendocrine carcinoma within the thyroid gland, characterized by strong invasiveness, high metastasis and recurrence rates. It is relatively rare among thyroid malignancies. The cytological and histological features of MTC are diverse and disperse, presenting as papillary, follicular, solid, trabecular, and spindle cell patterns. Immunohistochemical staining shows variable expression of calcitonin, carcinoembryonic antigen, and neuroendocrine markers. MTC can be classified into hereditary and sporadic types, with most cases caused by germline or somatic mutations in the RET gene located on chromosome 10. The 5th edition World Health Organization classification of endocrine and neuroendocrine tumors categorizes MTC into low-grade and high-grade based on tumor necrosis, mitotic figures, and Ki-67 proliferation index, highlighting that histological grading and RET gene mutations are independent prognostic predictors. This paper summarizes the recent advances in the pathological diagnosis of MTC, focusing on the key roles of the MTC grading system, molecular characteristics, and genetic screening and counseling in risk stratification for recurrence and targeted therapy.