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.

Case report of an infant with congenital mesoblastic nephroma leading to pulmonary metastasis.

Congenital mesoblastic nephroma is considered a tumour with favourable clinical behaviour with only few reported cases of metastases. We report an infant who underwent complete resection and later developed pulmonary metastasis. Ten-month-old baby girl initially presented at 3 weeks of age with macroscopic haematuria, hypertension and a lumbar mass. Contrast-enhanced computed tomography revealed a tumour arising from the left kidney without local invasion or metastasis. She underwent left nephrectomy. Immunohistochemistry confirmed a cellular type of congenital mesoblastic nephroma. At 10 months, she presented with difficulty in breathing. Contrast-enhanced computed tomography revealed an opacity in the right hemi-thorax. Histology of lung mass was suggestive of deposits from the previously excised mesoblastic nephroma. She developed a right-sided haemothorax and succumbed. This case report highlights the fact that even though congenital mesoblastic nephromas are considered tumours with favourable clinical behaviour, they can present later with distant metastasis. Therefore, clinicians need to be aware of this rare malignant potential and adhere to meticulous follow-up protocols.

A large pericardial cystic lymphangioma presenting as acute-onset respiratory distress in a child: a case report.

BACKGROUND: Lymphangiomas are rare benign malformations of the lymphatics that occur due to blockage of the lymphatic system during fetal development. They commonly occur in the neck and axilla, while involvement of the pericardium is rare. We report herein the case of a 16-month-old Sri Lankan child with a large pericardial cystic lymphangioma presenting with sudden-onset shortness of breath. CASE PRESENTATION: A 16-month-old Sri Lankan boy presented with sudden-onset dyspnea for 1-day duration following a febrile illness that lasted 2 days. On examination, he was afebrile and had subcostal, intercostal, and suprasternal recessions, with a respiratory rate of 50 breaths per minute. He had a loud expiratory grunt. The chest expansion was reduced on the right side, which was dull to percussion. Auscultation revealed a marked reduction of air entry over the right lower and mid zones. Chest X-ray showed a well-demarcated opacity involving the lower and mid zones of the right hemithorax associated with a tracheal shift to the opposite side. Ultrasound scan of the chest revealed fluid-filled right hemithorax suggesting a septate pleural effusion. A contrast-enhanced computed tomography scan of the thorax showed a large multiloculated extrapulmonary cystic lesion involving the right hemithorax with a mediastinal shift towards the left side associated with displacement of the right-side mediastinal structures. He underwent mini-thoracotomy and surgical excision of the cyst. A large cyst originating from the pericardium was observed and excised during surgery. Histological examination revealed a lesion composed of cysts devoid of a lining epithelium but separated by connective tissue, mature adipose tissue, and lymphoid aggregates. The child showed complete recovery postoperatively with full expansion of the ipsilateral lung. CONCLUSION: We report the case of a patient with cystic lymphangioma who was perfectly well and asymptomatic until 16 months of age. This case report presents the very rare occurrence of a large cystic lymphangioma originating from the pericardium. It highlights the importance of considering rare possibilities and performing prompt imaging in situations of diagnostic uncertainty to arrive at an accurate diagnosis that can be lifesaving.

Paediatric BCOR-associated sarcomas with a novel long spliced internal tandem duplication of BCOR exon 15.

Clear cell sarcoma of the kidney (CCSK) and primitive myxoid mesenchymal tumour of infancy (PMMTI) are paediatric sarcomas that most commonly harbour internal tandem duplications (ITDs) of exon 15 of the BCOR gene, in the range of 87-114 base pairs (bp). Some cases, instead, have BCOR-CCNB3 or YWHAE-NUTM2 gene fusions. About 10% of cases lack any of these genetic alterations when tested by standard methods. Two cases of CCSK and one PMMTI lacking the aforementioned mutations were analysed using Archer FusionPlex technology. Two related BCOR exon 15 RNA transcripts with ITDs of lengths 388 and 96 bp were detected in each case; only the 388 bp transcript was identified when genomic DNA was sequenced. In silico analysis of this transcript revealed acceptor and donor splice sites indicating that, at the RNA level, the 388-bp transcript was likely spliced to form the 96-bp transcript. The results were confirmed by Sanger sequencing using primers targeting the ITD breakpoint. This novel and unusually long ITD segment is difficult to identify by DNA sequencing using typical primer design strategies flanking entire duplicated segments because it exceeds the typical read lengths of most sequencing platforms as well as the usual fragment lengths obtained from formalin-fixed paraffin-embedded material. As diagnosis of CCSK and PMMTI may be challenging by morphology and immunohistochemistry alone, it is important to identify mutations in these cases. Knowledge of this novel BCOR ITD is important in relation to primer design for detection by sequencing, and using RNA versus DNA for sequencing.