The majority of the CCSKs in our cohort had BCOR ITDs, and none had the YWHAE-NUTM2 fusion. We verified the strong, diffuse cyclin D1 (CCND1) immunoreactivity in CCSKs described in recent reports. BCOR immunoreactivity was not consistently positive in all CCSKs with BCOR ITDs, and therefore cannot be used as a diagnostic immunohistochemical stain to identify BCOR ITD cases. The DN case was a BCOR-CCNB3 fusion sarcoma. BCOR-CCNB3 sarcoma is typically a primary bone sarcoma affecting male adolescents, and this is the first report of it presenting in a kidney of a young child as a CCSK. The full spectrum of DN CCSKs awaits more comprehensive characterisation.

Pathological diagnosis of clear cell sarcoma of the kidney (CCSK) is challenging as it resembles blastemal Wilms tumor (WT) and other pediatric sarcomas, and does not have any distinctive immunophenotype. The YWHAE-FAM22 translocation t(10;17)(q22;p13) has been reported in a subset of CCSK. This translocation also occurs in high-grade endometrial sarcoma, in which it is associated with cyclin D1 overexpression. Hence we seek to determine YWHAE-FAM22 translocation status and cyclin D1 immunoreactivity in a series of local CCSK cases. Of 8 CCSK cases from 7 patients identified, no CCSK had the YWHAE-FAM22 fusion transcript by reverse transcriptase-polymerase chain reaction. Novel karyotypes were identified for 2 cases: 1 had t(2;13)(q13;q22) and the other t(3:17)(q29;p11.2). Excluding a case with poor tissue section antigenicity, 7 of 7 CCSKs (100%) showed diffuse and strong nuclear cyclin D1 staining. Cyclin D1 immunohistochemistry was also performed on tissue microarrays of other pediatric renal tumors: blastemal areas of 18 WT cases were negative; 6 rhabdoid tumors and 1 metanephric adenoma showed patchy and weak staining; 3 mesoblastic nephromas and 18 of 29 neuroblastomas had positive staining. Cyclin D1 immunohistochemistry helps distinguish CCSK from blastemal WT and metanephric adenoma and rhabdoid tumors, but not from neuroblastomas and mesoblastic nephromas. Cyclin D1 overexpression in CCSK is not contingent on YWHAE-FAM22 translocation, and cyclin D1 inhibition may potentially be explored as a targeted therapeutic strategy in CCSK.

Congenital mesoblastic nephroma is characterised by kinase mutations including EGFR internal tandem duplications, the ETV6-NTRK3 fusion, and the rare KLHL7-BRAF fusion Aims: Congenital mesoblastic nephroma (CMN) is histologically classified into classic, cellular and mixed subtypes. The aims of this study were to characterise the clinical, pathological and molecular features of a series of CMNs, and to determine the utility of pan-Trk and epidermal growth factor receptor (EGFR) immunohistochemistry as surrogate markers for NTRK gene fusions and EGFR internal tandem duplications (ITDs). Methods and results: Twenty-two archival CMN cases (12 classic, five cellular, and five mixed) were tested for the ETV6-NTRK3 fusion and EGFR ITD transcripts by the use of reverse transcriptase polymerase chain reaction (PCR), and next-generation sequencing-based anchored multiplex PCR. All 12 classic CMNs had EGFR ITD. Of the five cellular CMNs, four had the ETV6-NTRK3 fusion and one had the KLHL7-BRAF fusion. Of the five mixed CMNs, four had EGFR ITD, and one had the ETV6-NTRK3 fusion. Pan-Trk immunoreactivity was 100% sensitive and 94.1% specific for the presence of NTRK rearrangement. However, EGFR staining was only 62.5% sensitive and 33.3% specific for EGFR ITD. Conclusions: EGFR ITD is a consistent genetic event in classic CMN. A majority of cellular CMNs have the ETV6-NTRK3 fusion. Rare cellular CMNs may harbour non-canonical mutations such as the KLHL7-BRAF fusion, which was found in one case. Mixed CMNs may have either EGFR ITD or the ETV6-NTRK3 fusion. Pan-Trk immunohistochemistry is a sensitive, albeit not perfectly specific, marker for NTRK rearrangement. EGFR immunohistochemistry is not helpful as a marker of EGFR ITD.

Introduction Primary spontaneous pneumothorax (PSP) and its high recurrence rate pose a therapeutic challenge to both patients and their managing surgeons. Mechanical or chemical pleurodesis can be used to prevent recurrence, but the optimal treatment often remains a matter of debate. This meta-analysis aims to compare the outcomes between mechanical and chemical pleurodesis following bullectomy for PSP. Materials and Methods Studies published up to 2019 were searched from Medline, Embase, Google Scholar, and Cochrane databases. A meta-analysis of randomized controlled trials (RCTs) and observational cohort studies (OCSs) comparing outcomes between mechanical and chemical pleurodesis for PSP was performed. Results Seven studies (one RCT and six OCSs) were included, comprising 1,032 cases of mechanical (799 abrasions, 202 pleurectomies, and 31 unspecified abrasions/pleurectomies/both), and 901 cases of chemical (643 talc, 69 minocycline, and 189 unspecified talc/kaolin) pleurodesis. The recurrence rate of pneumothorax after chemical pleurodesis (1.2%) was significantly lower than mechanical pleurodesis (4.0%) (pooled odds ratio [OR] = 3.00; 95% confidence interval [CI] = 1.59–5.67; p = 0.0007; I 2 = 19%). Hospital stay was also slightly shorter in the chemical pleurodesis group (pooled mean difference [MD] = 0.42 days; 95% CI = 0.12–0.72; p = 0.005; I 2 = 0%). There was no statistically significant difference in postoperative complications (pooled OR = 1.18; 95%CI = 0.40–3.48; p = 0.76; I 2 = 71%) and operative time (pooled MD = 3.50; 95%CI = − 7.28 to 14.28; p = 0.52; I 2 = 99%) between these two groups. Conclusion Chemical pleurodesis is superior to mechanical pleurodesis following bullectomy for PSP in reducing hospital stay and recurrence rate. However, more RCTs with longer follow-up are necessary to demonstrate the benefit of chemical pleurodesis for PSP.