Primary Osteosarcoma of the Sternum in a Child

Osteosarcoma is the most common malignant bone tumor of childhood, occurring particularly in the age group between 11 and 19 years¹. The prevalent site of this tumor is the metaphyseal portion of the long bones, especially in the distal third of the femur, followed by the proximal third of the tibia and, in third place, the proximal third of the humerus. These three sites account for approximately 80% of osteosarcomas in childhood.

Primary tumors of the sternum in childhood are very rare; they are generally malignant and comprise only 0.3% of sternal tumors in all age groups ². And while 7-8% of all bone tumors in children and adults occur in the chest wall, only 1% of these tumors arise from the sternum³. The purpose of this report is to discuss the management of a child with an unusual presentation of osteosarcoma.

Case Report

The patient was a 14-year-old teenage girl who presented three months prior to her admission to our institution with a mass over the sternum and progressive respiratory difficulty. On physical examination the patient appeared pale and had normal vital signs except for a respiratory rate of 65 per minute. A hard, fixed mass of 10 x 15 cm. was located over the superior region of the sternum and the patient was observed to be in respiratory distress. The initial chest X-ray demonstrated increased density as well as osteoblastic lesions in the sternum. The tumor was present throughout the extent of the sternum and extended into the mediastinum, although to a minimal extent (Figure 1). There were no abnormalities in the lungs. The chest CT scan showed complete involvement of the sternum by a mass of heterogeneous density containing multiple deposits of calcium as well as new bone formation, and confirmed the extension of the mass into the mediastinum (Figure 2). Bilateral pulmonary metastases were also observed. An open biopsy was performed and histopathological examination was consistent with a diagnosis of osteoblastic osteosarcoma. The patient was treated with neoadjuvant chemotherapy, which included cisplatin 120 mg/m² and doxorubicin at 90 mg/m², both on day one, alternating on week two with ifosfamide 13 gm/m². After six courses of this chemotherapy combination, a repeat CT scan of the chest demonstrated that the tumor size was reduced by 50% and now manifested areas of necrosis and additional calcification. Pulmonary metasteses persisted.

Figure 1. Chest X-ray showing a bone-forming mass in the sternum.

Figure 2. Chest CT scan, lateral view, demonstrating a solid osteoblastic tumor in the sternum.

Figure 3. Chest CT scan showing that the osteoblastic mass extends beyond the sternum and involves the lung parenchyma bilaterally

The patient was submitted to a complete surgical resection of the tumor mass and an external prosthesis was placed over the sternum. The pathology report at this time revealed 95% viable tumor with positive tumor margins. In the postoperative period the patient was given further chemotherapy with high-dose cyclophosphamide and carboplatin. However, after the first cycle was completed, and two weeks after the surgical procedure a repeat CT scan showed tumor regrowth (Figure 3). Shortly after, the patient developed sudden respiratory instability and respiratory failure with abrupt cardio-respiratory arrest resulting in death.

Discussion

Among the last 160 patients with osteosarcoma seen at the INP, this is the only patient with primary involvement of the sternum. It is generally considered that age at diagnosis (in children at least) is not a prognostic factor in osteosarcoma, but children under three, even though the disease is extremely rare in this age-group, could have an unfavorable prognosis⁴. The primary site of the tumor, however, is an important clinical prognostic factor⁵ and axial tumors are believed to have a poor outcome, at least in part because complete surgical resection is not possible in many of these patients. Another unfavorable prognostic factor that applies to the current patient is a tumor size of more than 15 cm. Probably even more significant for this patient was the finding that more than 10% of the tumor cells remained viable after neoadjuvant chemotherapy. Other prognostic factors worthy of mention are the overexpression of p-glycoprotein. This is encoded by the MDR1 gene, which is associated with resistance to chemotherapy in osteosarcoma ⁶ and the expression of epidermal growth factor receptor (HER2) ⁷. These markers were not measured in the present patient, but could well have been present.

The traditional therapeutic approach to osteosarcoma of the long bones cannot be used in patients with axial presentation. The current approach to osteosarcoma of the extremities is to administer neoadjuvant chemotherapy and resect the tumor, whenever possible, with placement of a prosthesis - providing that the surgical tumor margins are free of tumor cells. The demonstration that more than 90% of tumor cells are non-viable at the time of surgery is a good prognostic indicator. In patients with sternal tumors, unlike other axial forms of osteosarcoma, resection and the placement of a rigid prosthesis is possible, and is indicated when the patient is free of metastasis. This was not the case with the current patient.

From the surgical point of view it is of utmost importance to achieve a complete surgical resection in order to increase the probability of long-term survival. However, in patients with tumor involvement of the sternum, resection is associated with a significant risk of instability of the chest wall, which can eventually produce fatal respiratory failure, as was seen in our patient.

In summary the possibility of osteosarcoma should be considered in the presence of a tumor mass in the sternum. The initial use of neoadjuvant chemotherapy and early surgical resection by an experienced surgeon, follow by additional chemotherapy, is the treatment of choice.

Roberto Rivera-Luna,
National Institute of Pediatrics (INP), Mexico City, Mexico

References

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