Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in childhood. Here we studied 60 RMSs using whole-exome/-transcriptome sequencing, copy number (CN) and DNA methylome analyses to unravel the genetic/epigenetic basis of RMS. On the basis of methylation patterns, RMS is clustered into four distinct subtypes, which exhibits remarkable correlation with mutation/CN profiles, histological phenotypes and clinical behaviours. A1 and A2 subtypes, especially A1, largely correspond to alveolar histology with frequent PAX3/7 fusions and alterations in cell cycle regulators. In contrast, mostly showing embryonal histology, both E1 and E2 subtypes are characterized by high frequency of CN alterations and/or allelic imbalances, FGFR4/RAS/AKT pathway mutations and PTEN mutations/methylation and in E2, also by p53 inactivation. Despite the better prognosis of embryonal RMS, patients in the E2 are likely to have a poor prognosis. Our results highlight the close relationships of the methylation status and gene mutations with the biological behaviour in RMS.

No abstract

Sessile serrated adenoma (SSA), also referred to as sessile serrated polyp, has been proposed as a precursor lesion to microsatellite unstable carcinoma. However, the mechanism of stepwise progression from SSA to early invasive carcinoma has been unclear. The purpose of this study was to elucidate the histologic characteristics and possible role of p53, β-catenin, BRAF, KRAS, and PIK3CA in the development and progression of SSA. We analyzed 12 cases of SSA with neoplastic progression (SSAN), including 7 cases of intraepithelial high-grade dysplasia (HGD) and 5 cases of submucosal invasive carcinoma, and compared them with 53 SSAs and 66 hyperplastic polyps (HPs) by immunohistochemistry and gene mutation analysis. Histologically, 75% (9 of 12) of SSANs showed tubular or tubulovillous growth patterns rather than serrated ones in the HGD/intramucosal carcinoma component. All 5 SSANs with invasive carcinoma lost their serrated structure and developed increased extracellular mucin in their submucosal carcinoma component, a consistent feature of mucinous adenocarcinoma. Nuclear accumulations of β-catenin and p53 were observed in 50% (6 of 12) and 41.7% (5 of 12) of SSANs, respectively, and were exclusively present in HGD/carcinoma areas. By contrast, neither nuclear β-catenin nor p53 expressions were seen in HPs or SSAs (P<0.0001). BRAF mutations (V600E) were observed in 45.8% (11 of 24) of HPs, 60.9% (14 of 23) of SSAs, and 63.6% (7 of 11) of SSANs, and were equally found in both SSA and carcinoma/HGD areas of the individual SSANs. KRAS exon 1 mutations were uncommon in all 3 groups (4.2%, 4.4%, and 0%, respectively). No mutations of PIK3CA exon 9 or exon 20 were found in any cases that were examined. These findings suggest that BRAF mutations may be associated with the pathogenesis of SSA, but progression to HGD or early invasive carcinoma may be associated with other factors, such as alterations of p53 and β-catenin. In addition, our histologic observations suggest a possible close association between SSAN and mucinous adenocarcinoma.

No abstract

CIC-DUX4 and BCOR-CCNB3 fusion-gene-associated small round cell sarcomas account for a proportion of pediatric small round cell sarcomas, but their pathological features have not been sufficiently clarified. We reviewed a large number of soft tissue tumors registered at our institution, retrieved the cases of unclassified tumors with a small round cell component, and subjected them to histopathological, immunohistochemical, and gene profile analysis. We reviewed 164 cases of unclassified tumors with a small round cell component and analyzed them by RT-PCR and FISH. Tumors positive for a specific fusion-gene were also subjected to histopathological and immunohistochemical examinations. We identified 16 cases of BCOR-CCNB3/CIC-associated (CIC-DUX4 or CIC gene rearrangement-positive) sarcomas. These included seven BCOR-CCNB3 sarcomas and nine CIC-associated sarcomas. Heterogeneous elements included a myxoid spindle cell component in three BCOR-CCNB3 sarcomas and an epithelioid cell component in two CIC-associated sarcomas (one CIC-DUX4-positive and one CIC-DUX4-negative sarcomas). Mitotic activity was low in both heterogeneous components. By immunohistochemistry, in seven BCOR-CCNB3 sarcomas expression of EMA was positive in two cases, of p63 in three, of CD56 in six, of TLE1 in seven, of NKX2.2 in two, of CCNB3 in seven, and of BCOR in six cases (one case could not be tested for BCOR). In nine cases of CIC-associated sarcoma, CD56 was expressed in five, alpha-smooth muscle actin in one, ERG in three, and CD99, WT1 and TLE1 each in eight cases. Both sarcoma types showed not only a small round cell component, but also a myxoid/epithelioid component with low mitotic activity.