<strong>A Rare Case of Non Renal/ Non CNS Malignant Rhabdoid Tumor Originating from the Omentum</strong>
Creators: name: Ginsberg, Jessica
name: Wilson, John M
name: Linga, Vijay
name: Bhatt, Parth
name: Bhaskaran, Smita
name: Meller, Janet
Publisher: name: figshare
Year: 2023
Subjects: Paediatrics not elsewhere classified
Oncology and carcinogenesis not elsewhere classified

description: <strong>Introduction</strong>: Malignant Rhabdoid Tumor (MRT) is a rare malignancy in pediatric patients. These tumors typically originate in the kidney and central nervous system but may also arise from the liver, or other soft tissues. In our case 9 year old male presented with symptoms suggestive of complicated appendicitis and surgery showed the whole omentum studded with tumors and peritoneal carcinomatosis. The primary site of the tumor could not be established in spite of imaging with CT, MRI or PET-CT. <strong>Case Report</strong>: A 9-year-old male presented with abdominal pain in the right lower quadrant and suprapubic pain with vomiting and diarrhea for one week. The patient had fatigue for 3 weeks, fever and chills for 3 days. Patient had no past medical history and his family history included a grandmother with melanoma. The CT scan showed early appendicitis as well as diffuse omental thickening. There was also a solid and cystic appearing mass near the lower abdominal cavity measuring 5.7 X10.0 cm. The omental thickening may have been related to the lesion along the lower abdominal cavity. The patient underwent a diagnostic laparoscopy followed by conversion to exploratory laparotomy with appendectomy and omentectomy. The finding was carcinomatosis in the abdomen. The omentum was studded with small nodules, which appeared abnormal. There was also bloody fluid in the gutters. Most of the tumor in the right iliac fossa, appendix and omentum was debulked. Pathological examination demonstrated solid sheets, nests and cords of malignant cells with abundant eosinophilic cytoplasm. Nuclei were large, pleomorphic, and vesicular. Immunoperoxidase stains were positive for pancytokeratin, EMA, vimentin, and CD99. The patient was diagnosed with Non Renal/ Non CNS MRT. No other sites were involved. Post surgery MRI and PET-CT showed sill disease activity in most of the peritoneum. A multidisciplinary treatment approach was planned with four cycles of chemotherapy followed by surgery and radiotherapy. As per the COG guidelines chemotherapy with Ifosfamide/ carboplatin/ Etoposide alternating with Vincristine/ Doxorubicin / cyclophosphamide was planned. Chemotherapy complications included pancytopenia, nausea, vomiting, ifosfamide neurotoxicity, Fanconi syndrome and hemorrhagic cystitis. He completed three cycles of chemotherapy with interim PET –CT showing partial response with tolerable toxicity. <strong>Discussion</strong>: Malignant rhabdoid tumors (MRT) are aggressive tumors most often found in pediatric patients originating from the kidney. These tumors have also been found to originate form the central nervous system (referred to as atypical teratoid tumors), the liver, and soft tissues. Patients who are younger than 3 years old have been found to have a worse prognosis. Malignant rhabdoid tumors originating from the omentum is a very rare occurrence. The omentum is often a location of tumor metastasis but is seldom the primary location of a tumor. Symptoms of omental involvement include abdominal discomfort, abdominal mass, and abdominal distension. Histological examination of MRTs will reveal sheets of rhabdoid cells. Rhabdoid cells are polygonal cells with vesicular nuclei, prominent nucleolus, and cytoplasm containing eosinophilic, hyaline inclusions that are PAS-positive. On immunohistochemical analysis, MRTs stain for vimentin, cytokeratin, and EMA. The development of MRT is associated with deletion or mutation of the SMARCB1 gene (hSNF5/INI1/BAF47) on chromosome 22q. Testing for a SMARCB1 deletion or mutation or the absence of its products can be used for a more accurate diagnosis. SMARCB1 is a tumor suppressor gene. Loss of this gene leads to deregulation of the cell signaling pathways including CDK/CDK6/cyclinD1, aurora kinase A, and the Sonic hedgehog pathway. <strong>Conclusion</strong>: Non Renal/ Non CNS MRT is a rare presentation. In our case omentum was the primary site. A multidisciplinary treatment was planned. There was good partial response to chemotherapy with tolerable toxicity.