|Year : 2012 | Volume
| Issue : 3 | Page : 424-426
Extra osseous osteosarcoma of the retroperitoneum: An unusual entity
Ranganath Ratnagiri, Vivek Garg, Rashmi Chaturvedi
Department of Surgical Oncology, Lucknow Cancer Institute, Hazratganj, Lucknow, India
|Date of Web Publication||17-Nov-2012|
Consultant Surgical Oncologist, Lucknow Cancer Institute, Hazratganj, Lucknow
Source of Support: None, Conflict of Interest: None
Extra-osseous osteosarcomas constitute about 1-1.2% of all osteosarcomas. The most common sites are the extremities, thorax, and the abdomen. Retroperitoneal osteosarcomas are rare and very few cases have been reported. They are similar in their biology to high grade soft tissue sarcomas. R0 resection appears to be the best possible treatment for these tumors. All three variants of conventional osteosarcoma-osteoblastic, chondroblastic, and fibroblastic have been described in these tumors. Chemotherapy has been attempted with adriamycin-based regimens with poor results. Unlike extremity osteosarcomas, these tumors have been found to be chemoresistant. The 5 year survival has ranged from a dismal 12% to about 25%. We report a 46-year-old male who presented with a kidney tumor infiltrating the descending colon, but turned out to be an extra osseous osteosarcoma. An R0 resection was done and adjuvant chemotherapy given.
Keywords: Extra osseous osteosarcoma, R0 resection, retroperitoneum
|How to cite this article:|
Ratnagiri R, Garg V, Chaturvedi R. Extra osseous osteosarcoma of the retroperitoneum: An unusual entity. J Can Res Ther 2012;8:424-6
| > Introduction|| |
Extraosseous osteosarcoma (EOO) is a malignant mesenchymal neoplasm located in the soft tissues without direct attachment to the skeletal system, and produces osteoid, bone, or chondroid material. The first case of EOO was reported by Wilson in 1941.  These tumors are rare entities and constitute about 1.2% of all soft tissue sarcomas.  Since their first description in 1941, only about 300 cases have been reported in world literature, with the largest series being of 40 cases over a 73-year period.  Consequently, their biological behavior and response to treatment are yet to be fully understood.
What is, however, known about these tumors is that they occur most commonly in the soft tissues of the extremities with the thorax being the second most common site. Only a handful of cases have been reported with the retroperitoneum as the primary site.  Retroperitoneal extra-osseous osteosarcomas usually present with synchronous pulmonary metastases. The tumor itself is usually locally aggressive and presents with invasion of the surrounding structures. An R0 resection, if possible, is the best initial modality of treatment. Chemotherapy has been attempted, though with poor results.
| > Case Report|| |
A 46 years, presented to us with complaints of abdominal pain, distention, and vomiting. Clinical examination revealed a bimanually palpable mass in the left lumbar region along with signs of sub-acute intestinal obstruction. There were no clinically evident metastases and the hemodynamic status was stable.
A computerized tomographic (CT) scan of the abdomen revealed a tumor arising from the lower pole of the left kidney, infiltrating the descending colon. There were no liver or lung metastases, nor retroperitoneal nodes.
Fluid electrolyte imbalance was corrected and the patient was taken up for semi emergency laparotomy. Intra operatively, we found a large tumor arising from the left kidney infiltrating into the lumen of the descending colon and causing dilatation of the proximal bowel. A left radical nephrectomy with resection of the descending colon in toto was performed. An end to end colo-colic anastomosis was fashioned along with a diverting colostomy. The patient's recovery was slow but uneventful.
On gross pathologic examination, the tumor had a lobulated and fleshy appearance with brownish areas on the periphery. Foci of necrosis and hemorrhage were obvious throughout the tumor and extensive areas were hard and calcified.
Microscopy showed large malignant elongated spindle cells with pleomorphic nuclei [Figure 1] arranged in an irregular fascicular pattern. There were numerous multinucleated and bizarre cells with a number of atypical mitoses. The stroma was highly cellular. The striking microscopic feature of the tumor was the presence of abundant malignant osteoid [Figure 2]. The tumor was highly vascular with focal necrosis and inflammatory infiltrates.
|Figure 2: Malignant cells with osteoid and interspersed glomeruli (H&E 10×)|
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All the resected margins were microscopically free of tumor.
These microscopic features lead to a pathologic diagnosis of extra-osseous osteosarcoma (osteoblastic variant).
The patient received six cycles of adjuvant adriamycin-based chemotherapy (adriamycin-ifosfamide combination). However, he developed bilateral pulmonary metastases 6 months after completion of chemotherapy and succumbed to the disease.
| > Discussion|| |
Extraosseous osteosarcomas are uncommon tumors, which can arise in various sites. The thigh and gluteal muscles are the most common areas of occurrence.  The thorax and the retroperitoneum are next in incidence. These tumors occur in the sixth to seventh decades and have a male predominance.  Retroperitoneal tumors are extremely rare and only a few cases have been reported.
Retroperitoneal osteosarcomas have a range of clinical presentations. Most are asymptomatic for the primary tumor but present with features of pulmonary metastases.  There are tumors which present with pressure symptoms or as a rapidly growing mass. Intestinal obstruction as a complication has not been reported as yet. Preoperative diagnosis is usually of a retroperitoneal sarcoma and surgery is the treatment of choice, provided the tumor is operable and nonmetastatic. 
The gross pathologic appearance varies with the consistency ranging from soft to hard. There usually is a pseudo capsule surrounding the tumor, with central necrosis being a common feature.  Microscopy shows a sarcomatous stroma, with malignant spindle cells. Pleomorphic and bizarre forms are also seen, as are atypical mitoses.  The clinching evidence in favor of an extra-osseous osteosarcoma is the demonstration of malignant osteoid in the stroma. 
All the three pathologic variants: Osteoblastic, chondroblastic, and fibroblastic, have been described in this entity too. The presence of malignant osteoid helps in differentiating these tumors from other soft tissue sarcomas and radiologically similar conditions like myositis ossificans. 
These tumors have an aggressive biological course and usually present with pulmonary metastases.  If nonmetastatic, radical resection appears to be the best course of treatment. Adriamycin-based chemotherapy has been attempted, with poor results.  The regimes which have been tried are those in use for soft tissue sarcomas or variations thereof.  Adjuvant therapy is given on the basis of tumor size, grade, mitotic index, and the extent of tumor necrosis.  External beam radiotherapy has been attempted in the preoperative setting and as an adjuvant, but without demonstrable increase in disease free survival.  Brachytherapy has been tried only in the setting of a clinical trial.  The 5 year survival rates ranged from 25% to 37%. 
In conclusion, extra-osseous osteosarcomas are uncommon and aggressive tumors, which are best treated by radical surgery. Local recurrences and metastases are common, and lead to a poor prognosis in these patients.
The patient completed 6 cycles of adriamycin - ifosfamide chemotherapy. However, he succumbed to pulmonary metastases six months after completion of treatment.
| > References|| |
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[Figure 1], [Figure 2]