Extrarenal Rhabdoid Tumour of Soft Tissue

Citation: Plasschaert H, Deman F, Bempt IV, Labarque V, Aertsen M, et al. (2020) Extrarenal Rhabdoid Tumour of Soft Tissue. Int J Pathol Clin Res 6:105. doi.org/10.23937/2469-5807/1510105 Accepted: March 12, 2020: Published: March 14, 2020 Copyright: © 2020 Plasschaert H, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Fluorescent in situ hybridisation on formalin fixed paraffin embedded material of the tumour showed no evidence for EWSR1 rearrangement (to exclude Ewing sarcoma). There was no loss of SMARCB1/INI1 in the PDGFB region (22q11) and no ETV6-NTRK3 rearrangement was found (excluding congenital fibrosarcoma). Eventually Next Generation Sequencing on the FFPE material showed a pathogenic nonsense mutation c.842G > A (p.Trp281 * ) in SMARCB1, ascertaining the diagnosis of a malignant rhabdoid tumour. Additionally, a heterozygous c.842G > A (p.Trp281 * ) nonsense mutation, causing a premature stop codon, was found in a blood sample of the patient. This mutation is seen in Rhabdoid Tumour Predisposition syndrome (RTPS). Three months after birth, palliative support was initiated because of progressive disease despite chemotherapy.
Malignant rhabdoid tumour is best known in the kidney and the central nervous system but primary lesions may appear in other organs, skin and soft tissue [1,2]. Extrarenal rhabdoid tumours of soft tissue are highly aggressive and seem to be confined almost exclusively to children. Congenital cases are reported in the literature and rhabdoid tumour predisposition syndromes 1 and 2 (RTPDS 1 and 2) have been described [3][4][5]. Most often extrarenal rhabdoid tumours of soft tissue present in a deep axial location, the neck or paraspinal [1].

Case Report
Extrarenal rhabdoid tumours appearing in the soft tissues are very rare and might be confused with other high-grade sarcomas harbouring rhabdoid features. We present a case and highlight the differential diagnosis, the ancillary techniques necessary to define its true rhabdoid nature, and the existence of hereditary syndromes.
Our case concerns a new-born boy with a congenital and rapidly growing mass in the soft tissue of the left thoracic wall, expanding from a few cm in diameter at the time of birth, to a mass measuring more than 20 cm after one month. Imaging based on US and MRI revealed a large soft tissue tumour invading the pleura of the left lung ( Figure 1). Additional PET/CT demonstrated spread of the disease in the spleen, lymph nodes, muscle, cerebellum, skin and bone.
Needle biopsy revealed a solid tumour with collagenous to myxoid background, sheets and nests of pleiomorphic epithelioid cells with high mitotic activity. The nuclei were irregular and vesicular. The cytoplasm varied from clear to densely eosinophilic (Figure 2a). The initial histological differential diagnosis concerned Ewing sarcoma, congenital fibrosarcoma, pleuropulmonary blastoma, synovial sarcoma and rhabdoid tumour of soft tissue. Immunohistochemistry for CD 99, alfa smooth muscle actin and p53 was positive, there was faint and variable expression of keratins and s100. De-     sarcomas and should not be a feature of rhabdoid tumours. Epithelioid sarcoma appears more often in older patients and thus the age of the patient could be the only discerning factor.
Patients with malignant rhabdoid tumour of soft tissue present at a young age, often with disseminated disease and the aggressive course of the disease is most often fatal [1]. Patients presenting with multiple lesions, congenital disease or in the first years of life might suffer from hereditary syndromes RTPDS1 or 2. It is suspected that up to 35% of malignant rhabdoid tumours are caused by a germline mutation. RTPDS1 is an autosomal dominant condition caused by mutations in SMARCB1 (22q11.23), leading to malignant renal and extrarenal rhabdoid tumours and tumours of the central nervous system (e.g. hereditary schwannomatosis).
Mutations causing inactivation or loss of the SMARCB1 gene (also known as INI1) on chromosome 22, deletions or translocations involving 22q11.2 and subsequent loss of INI1 expression by immunohistochemistry are essential for the diagnosis. These alterations are found in more than 90% of extrarenal rhabdoid tumours and in rhabdoid tumours of the kidney and central nervous system [1].
They are usually not found in other sarcomas harbouring areas of rhabdoid dedifferentiation except for epithelioid sarcomas [6]. These lesions may show (predominant) rhabdoid morphology on histological examination, show expression of vimentin and keratins (e.g. EMA) and distinction between epithelioid sarcoma and extrarenal rhabdoid tumour can be difficult, if not impossible. CD34 is expressed in about 40% of epithelioid