Clear Cell Variant of Embryonal Rhabdomyosarcoma: Report of an Unusual Retroperitoneal Tumor—Case Report and Literature Review

Case Report A 4-year 8-month-old female presented with 5 months history of emesis, abdominal pain, night sweats, weight loss (5 pounds, 2267.96 g), and fullness of left upper abdominal quadrant noted by parents on the day of admission. On examination, the abdomen showed a large firm 10 × 10 cm mass in the above area with another 4 × 4 cm mass in the right upper quadrant. Further systemic examination was normal. Complete blood counts were normal. Alanine transaminase (470 U/L), aspartate transaminase (470 U/L), amylase (417 U/L), lipase (564 U/L), and bilirubin (89 g/L) were elevated. Urinary catecholamines, α-fetoprotein (AFP), and β-human chorionic gonadotropin (hCG) values were normal. Magnetic resonance imaging (MRI) of the abdomen showed a large retroperitoneal mass 10 × 13 × 14 cm in size intimately associated with the left lobe of the liver, encasing the hepatic artery origin. There was a tumor thrombus in the common bile duct causing enlargement of the gall bladder as well ([ Fig. 1 ]). A solitary nonocclusive thrombus was also seen in the portal vein. Bone marrow aspiration and biopsy were clear of malignancy. Full body bone scan showed no evidence of tumor involvement. A laparoscopy with biopsy of the tumor was performed 4 days after admission. Intraoperatively, extensive dissemination of tumor throughout abdomen along with omental seeding was noted. Figure 1 MRI at diagnosis and after treatment. (A and B) Axial and coronal MRI HASTE images depicting large heterogeneous mass in the epigastric region, adjacent to the liver (L), separate from spleen (S), and pancreas (P) with tumor extension into the common bile duct (block arrow), and dilatation of the bile ducts. (C) MRI HASTE postchemotherapy image demonstrates moderate reduction in tumor size with resolution of biliary ductal tumor and dilatation (line arrow). HASTE, half-Fourier acquisition single-shot turbo spin echo; MRI, magnetic resonance imaging. Histopathology showed nodules and sheets of clear cells and minimal spindle cells as well as undifferentiated basophilic cells admixed with focal round strap and tadpole-shaped eosinophilic rhabdomyoblasts. Aberrant mitoses and karyorrhexis were present. Immunohistochemistry showed desmin positivity and a proliferation activity (MIB1 or Ki67) of 40% with negativity of neuron-specific enolase, pan-keratin markers for epithelial cell differentiation, AFP, hCG, and chromogranin A for endocrine differentiation. Myogenin (MYF4) was positive ([ Fig. 2a–d ]). The Children's Hospital follows strict criteria of quality assurance and the diagnosis was reviewed and confirmed according to Children's Oncology Group protocols in the North-American Review Panel for pediatric tumors. Figure 2 (a–d) Rhabdomyosarcoma consisting of small, round, or spindle-shaped cells in an abundant myxoid stroma highlighting and mimicking a clear cell pattern (a) (hematoxylin-eosin staining, original magnification: 400×). Focally, tumor cells were admixed with a small number of round, strap- or tadpole-shaped eosinophilic rhabdomyoblasts (b, arrows) (hematoxylin-eosin staining, original magnification: 400×) showing expression for desmin (c) (avidin-biotin complex technique for immunohistochemistry using a monoclonal antibody against the antigen desmin, original magnification: 630×) and MYF4 (d) (avidin-biotin complex technique for immunohistochemistry using a monoclonal antibody against the antigen MYF4, original magnification: 200×). Ultrastructural analysis (e and f) confirms the presence of sarcomeric complexes Z striae (arrows) as well as rigid thick (myosin) filaments along and between which are ribosomes. Some sarcomeric complexes showed good organization, while in other fields disorganization of the sarcomeric complexes was more prominent. Some glycogen accumulation was also found (Hitachi transmission electron microscope, original magnifications: 4000× for e and 1500× for f). MYF4, myogenin. Electron microscopy showed loose array of fusiform cells in a collagenous-like matrix. Tumor cells showed sarcomatoid formation with contractile filaments (alternating thick and thin filaments with Z-bands) substantiating the light microscopy features. Cells also contained a large amount of glycogen and dilated cisterns of rough endoplasmic reticulum. No alveolar pattern of rhabdomyosarcoma was detected ([ Fig. 2e, f ]). At the pediatric tumor board therapy options for this stage IV metastatic embryonal rhabdomyosarcoma, clear cell variant were discussed. The child was started on intensive multiagent chemotherapy with dose compressed 2 weekly alternating cycles of vincristine, doxorubicin, cyclophosphamide, and etoposide/ifosfamide. This was continued for 16 weeks. Interim assessment with reimaging showed a lack of major response to therapy and absence of significant tumor shrinkage. Thereafter, the patient received weekly vincristine along with 3 weekly irinotecan for the next 10 weeks. There were ongoing and incremental delays in administration of chemotherapy due to the intensively myelo-suppression of this chemotherapy and delays in recovery of bone marrow and the blood counts. The tumor continued to be fluorine-18-fluorodeoxyglucose (FDG) avid on positron emission tomography. With minimal response to chemotherapy, the patient was considered to be unresectable. Hence, after radiotherapy planning by tomotherapy, she received a total of 45 Gy in 28 fractions to achieve some tumor shrinkage and surgical resectability. The tumor did shrink marginally, however the shrinkage was not very significant and further radiation therapy was avoided respecting the tolerance of critical organs, especially the kidneys. Once again, the patient was evaluated for surgical resection. During surgery, no evidence of metastatic disease was found in the abdomen. The initially identified metastasis plausibly responded to combination chemotherapy and radiation therapy that was administered before surgery. Intraoperatively, the tumor was large, bilobed, tan-colored, 12 cm in maximum diameter and arose from the retroperitoneum, extended through the lesser omentum and was adherent to portal vein, hepatic artery, and caudate lobe of liver. The tumor was dissected off the portal structures and resected without rupture or spill along with segmental resection of the caudate lobe of liver. The surgical margins were clear and the patient was in complete remission (CR). Thereafter the patient received consolidation therapy in the form of high dose myeloablative chemotherapy followed by autologous stem cell transplant. The high dose chemotherapy consisted of thiotepa (3 days) and melphalan (2 days) and was followed by stem cell infusion. The patient engrafted on day +8 of stem cell infusion. Post stem cells, the patient was aggressively managed for grade IV mucositis, infection control and prophylaxis, nutritional support and with supportive care as per standard institutional protocols. She did not suffer any major complications apart from mucositis. She continues to do well clinically and is 5 months post stem cell transplant in CR without any major complications. Although there was a tumor thrombus in the biliary duct it did not lead to biliary obstruction and resolved by itself with therapy.

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