[Clinicopathological characteristics of NTRK-rearranged mesenchymal tumors in childhood].

Objective: To investigate the clinical and pathological features of pediatric NTRK-rearranged tumors. Methods: Four NTRK-rearranged soft tissue tumors and one renal tumor at Shanghai Children's Medical Center, Shanghai Jiaotong University and Singapore KK Women's and Children's Hospital from January 2017 to September 2019 were identified. Pan-TRK immunohistochemistry, and the ALK and ETV6 gene break-apart fluorescence in situ hybridizations (FISH) were performed. NTRK gene rearrangement was detected using sequencing-based methods. Results: There were 3 males and 2 females in this study. The patients were between 3 months and 13 years of age. Histologically, the tumors were infiltrative spindle cell tumors with variable accompanying inflammatory cells. Immunohistochemistry showed positive reactivity for pan-TRK in all tumors, with nuclear staining for NTRK3 fusion, and cytoplasmic staining for NTRK1 fusion. The molecular testing revealed NTRK gene fusions (one each of TPM3-NTRK1, ETV6-NTRK3 and DCTN1-NTRK1, and two cases of LMNA-NTRK1). Two patients were receiving larotrectinib. The others were are well without disease, with follow-up durations of 9 to 29 months. Conclusions: NTRK-rearranged mesenchymal tumors from soft tissue sites and kidney are identified. A novel DCTN1-NTRK1 fusion is described. Pan-TRK immunohistochemistry is useful for diagnosis. NTRK-targeted therapy may be an option for unresectable, recurrent or metastatic cases.

[Eosinophilic solid and cystic renal cell carcinoma with TSC2 gene mutations in children].

Objective: To study clinical pathological characteristics, immunohistochemical, molecular genetical changes and prognosis in pediatric eosinophilic solid and cystic renal cell carcinoma (ESC RCC) with TSC2 gene mutations. Methods: The tissue samples were collected from two pediatric ESC RCC patients between 2017 and 2018. The tissues were subjected to histological examination and immunohistochemistry using EnVision system. The TFE3, TFEB gene rearrangements were tested using FISH and molecular genetic study. The paraffin sections were used for DNA extraction, PCR amplification and NGS sequencing. Results: The two patients with ESC RCC were both male, aged at 9 years and 8 months, and 13 years, respectively. The tumors were from the right kidney, 5 cm and 7 cm in size, respectively, with solid and cystic changes in cross section, and grey-reddish or grey-whitish fish meat appearance. Microscopic observation revealed the tumors had fibrous capsules, which were infiltrated by the tumor cells. The tumor cells were diffusely distributed, round-shaped, or polygon-shaped, and had voluminous cytoplasm, eosinophilic cytoplasm, various sizes of vacuoles and clear cell-like appearance. There were papillary structures in some areas, with visible fiber septa. The nuclei were round and vesicular, with multi-nucleated cells and megakaryocytes. The mitoses were not seen. A few cystic structures were visible in different sizes, and capsule walls were covered with a single layer of spike-like tumor cells. Thick-walled blood vessels were seen in the stroma, with focal lymphocytic infiltration, eosinophilic necrosis, calcifications and cholesterol crystals. Immunohistochemistry of the tumor cells was positive for PAX8 (diffuse), CK20 (focal), CKpan (focal), CK10 (1 focal, 1 diffuse), INI1, vimentin, CD68, and Ki-67 (5%~10%); the tumor cells were negative for HMB45, S-100, Melan A, p53, desmin, TFE3, CK7, CK19, EMA, CD56, CgA, Syn, CD30, CD117, WT1 and SMA. Molecular genetic study showed that TFE3 and TFEB gene rearrangements were not detected by FISH. NGS sequencing showed TSC2 p.Lys574Ter (0.198) was found in patient one and TSC2 p.Arg406Ter (0.355) in patient two. Conclusions: ESC RCC in children is a rare disease, and can be misdiagnosed easily. It has unique pathological characteristics, and immunohistochemical, molecular and genetic changes. The prognosis is relatively good.

Cells with ganglionic differentiation frequently stain for VE1 antibody: a potential pitfall.

Mitogen-activated protein kinase (MAPK) pathway plays a major role in pediatric low-grade gliomas (pLGGs). Immunohistochemistry with mutant-specific antibody, VE1, has appeared to be the most affordable and rapidly deployable method to identify tumors with aberrant MAPK signaling pathway, by highlighting tumor with BRAFV600E mutation. Nonetheless, positive staining cases but not associated with BRAFV600E mutation are also seen. We analyzed 62 pLGGs for the two commonest genetic aberrations in MAPK pathway: KIAA1549-BRAF fusion, using reverse-transcriptase polymerase chain reaction, and BRAFV600E mutation, using VE1 antibody and Sanger sequencing. We recorded a specificity and accuracy rate of 68.75% and 75%, respectively, for VE1, when strong cytoplasmic staining is observed. Interestingly, we observed that cells with ganglionic features frequently bind VE1 but not associated with BRAFV600E mutation. Such observation was also confirmed in four cases of differentiating neuroblastoma. This false positive staining may serve as an important confounder in the interpretation of VE1 immunoreactivity with major therapeutic implication. It is important to confirm the presence of BRAFV600E mutation by DNA-based method, especially in tumor entities not known to, or rarely harbor such mutations.

A rapidly fatal intracranial anaplastic hemangiopericytoma with de-novo dedifferentiation: emphasis on diagnostic recognition, molecular confirmation and discussion on treatment dilemma.

Solitary fibrous tumors/ hemangiopericytomas (SFT/HPC) are mesenchymal tumors that share a common genetic aberration and very rarely undergo dedifferentiation. We report a unique case of an intracranial anaplastic SFT/HPC with de-novo dedifferentiation, which pursued a rapidly fatal clinical course in a 41-year-old lady. The dedifferentiated component comprised a focal area of glandular formation with epithelial immunophenotype acquisition. The distinct biphasic pattern of the tumor imparted great diagnostic challenges to the pathologists. An increased awareness of SFT/HPCs with a diverse morphologic spectrum or even a biphasic histologic pattern is essential in working up such cases. We first attempted gamma knife radiosurgery in treating a recurrent dedifferentiated SFT/HPC; unfortunately it was to no avail. Although it is now known that SFT/HPC is characterized by NAB2-STAT6 gene fusion, the unavailability of targeted therapy against this molecular signature still results in a treatment dilemma.

Rosai-Dorfman disease of the testis: an unusual entity that mimics testicular malignancy.

A 47 year old Chinese man with diabetes mellitus and previously treated pulmonary tuberculosis presented with painless right testicular enlargement of 1 month's duration. He underwent an orchidectomy for presumed testicular neoplasm corroborated clinicoradiologically. Histological examination of the testicular mass revealed an inflammatory lesion comprising lymphocytes, plasma cells and sheets of pale staining histiocytes, some containing lymphocytes within their ample cytoplasm, suggestive of emperipolesis. S100 immunohistochemistry stained the histiocytes, while ultrastructural examination confirmed emperipolesis. A diagnosis of Rosai-Dorfman disease was made, an exceedingly rare testicular lesion. Clinicoradiological findings mimicked a neoplasm, while the inflammatory histological appearances with occasionally discerned multinucleated cells raised the possibility of xanthogranulomatous orchitis. Tuberculous orchitis was excluded through negative Ziehl-Neelsen stains and PCR for mycobacterium, while seminoma, which sometimes features a predominant inflammatory component obscuring neoplastic cells, was excluded by absent immunostaining for placental alkaline phosphatase and CD117.

Pseudomembranous trigonitis in a male with Klinefelter syndrome: a case report and evidence of a hormonal etiology.

Klinefelter syndrome is a clinical syndrome with a distinct 47, XXY karyotype. Patients are characterized by a tall eunuchoid stature, small testes, hypergonotrophic hypogonadism, gynecomastia, learning difficulties and infertility. These patients have also been found to have raised estrogen levels. We report a 16 year old boy with Klinefelter syndrome presenting to our institution with gross hematuria. Cystoscopy and biopsy revealed the diagnosis of pseudomembranous trigonitis. Immunohistochemical stains showed an increase in estrogen and progesterone receptors in the trigone area but not in the rest of the bladder. In view of the patient's mildly raised estrogen levels and the histological findings, we postulate that estrogen is the driver of the development of pseudomembranous trigonitis. This is the first reported case of pseudomembranous trigonitis seen in association with Klinefelter syndrome, and also the first case of pseudomembranous trigonitis occurring within the male adolescent age group.