What Is the Best Treatment of Malignant Bone Tumors in Children?

Published on 11/03/2015 by admin

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Chapter 38 What Is the Best Treatment of Malignant Bone Tumors in Children?

SYSTEMIC THERAPY

The two most common primary tumors of bone are osteosarcoma (OS) and Ewing’s sarcoma (ES) with an incidence of 4.8 cases/million and 2.9 cases/million, respectively, in people younger than 20 years.1 ES is part of a family of small, round, blue cell tumors whose exact cell of origin remains unknown. The mainstay of therapy includes multiagent cytotoxic chemotherapy and effective local control with surgery and/or radiation. The following section focuses on the medical therapy of localized OS. Improvement in the survival of patients with OS has been elusive since the therapeutic breakthroughs of the late 1970s to early 1980s, despite the efforts of large multinational cooperative groups.

CHEMOTHERAPY IN OSTEOSARCOMA

It is clear that with surgery alone, 80% of patients with malignant bone tumors will develop pulmonary metastases.2 Therefore, the treatment of OS has evolved to include systemic chemotherapy in addition to surgical resection. OS is relatively resistant to radiotherapy, so this particular modality is not used with curative intent. With current chemotherapy regimens, event-free survival remains at approximately 70% at 5 years.

Multiple fundamental issues regarding the treatment of OS remain incompletely resolved:

Since the late 1980s, many centers have conducted trials to attempt to answer the above questions. However, many studies are uncontrolled case series that document the outcomes of a given treatment according to an institutional protocol.

Does Tailoring Postsurgical Chemotherapy According to the Degree of Tumor Response Improve Survival?

One advantage to neoadjuvant (pre-operative) chemotherapy is the opportunity provided for assessment of the tumor’s response to the drugs being administered. Histologic assessment of the tumor after resection is most commonly described as per the Huvos system. A major distinction is drawn between tumors in which there are fewer than 10% residual viable cells and those with more than 10%.9 The degree of histologic response to chemotherapy is of prognostic relevance with “responders” (patients >90% necrosis) having significantly better outcome than “nonresponders” (patients <90% necrosis). It is less clear whether changing the therapeutic regimen in patients with poor response will improve survival. Unfortunately, all studies that have attempted to address this question have been single-arm case series. None of these studies demonstrated the ability to salvage patients who had a poor response by an alteration in postoperative therapy.1013 Currently, an international study is under way to address this question in a randomized fashion.13a

LOCAL CONTROL

The current basic principles for the surgical management of malignant pediatric musculoskeletal tumors were developed approximately 25 to 30 years ago when limb salvage surgery became commonly feasible. The primary basis for these principles included case series, anecdotes, and expert opinion. These principles are not disputed in the main, so few comparative studies challenge them directly. Techniques developed in this manner include safe biopsy principles and the necessity for wide en bloc resection. Here, we consider only those issues relating to local control for which there is at least Level III evidence and where the study population at least substantially involves skeletally immature patients. Comparative studies in musculoskeletal tumor surgery are primarily focused on reconstruction of defects after en bloc resection.

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