For tumor staging of both benign and malignant lesions of bone and soft tissue by orthopedic oncologists, the staging system of the MSTS (Musculoskeletal Tumor Society), also known as the Enneking staging system, is commonly used. The TNM staging system is also popular but will not be further discussed in this chapter.
The MSTS system includes separate classifications for benign bone tumors and malignant tumors of bone or soft tissue.
The Musculoskeletal Tumor Society staging system for benign bone tumors classifies the tumor as:
1 – latent
2 – active
3 – aggressive
Latent tumors (e.g., non-ossifying fibroma) have well-demarcated borders, are slow growing, are contained within the medullary canal, may remain stable or occasionally involute spontaneously, and have a low recurrence rate following intralesional surgery.
Active lesions (e.g., chondromyxoid fibroma) also have well-defined borders but, considering active growth, cause cortical thinning without extension beyond the cortex.
Aggressive lesions (e.g., giant cell tumor of bone) have indistinct margins within the bone and have grown beyond the limits of the bone and into surrounding soft tissues. These lesions also have a higher recurrence rate following intralesional surgery.
The Musculoskeletal Tumor Society staging system for malignant musculoskeletal tumors considers any tumor with known metastases to be Stage III. Among those without known metastases, tumors with low-grade histology are Stage I and high-grade tumors are Stage II.
Stage I and Stage II are further subclassified as either intra- or extra-compartmental, based on whether the tumor has extended beyond its anatomical confines, e.g., the bone or a fascial plane encompassing muscle.
Most osteosarcomas, for example, are Stage IIB at diagnosis with tumor originating within a bone but then extending beyond the bone to the surrounding soft tissues without the presence of visible distant metastases.
The full staging system is as follows:
- Stage IA: low-grade, no metastasis, intra-compartmental
- Stage IB: low-grade, no metastasis, extra-compartmental
- Stage IIA: high-grade, no metastasis, intra-compartmental
- Stage IIB: high-grade, no metastasis, extra-compartmental
- Stage III: metastasis present, independent of grade
Treatment of Musculoskeletal Tumors
There are several potential treatment options for musculoskeletal tumors. For those lesions in bone, these range from simple curettage to aggressive intralesional excision to wide and radical resection.
Simple curettage is sufficient for lesions which tend to be self-limited such as non-ossifying fibroma and eosinophilic granuloma.
Aggressive benign lesions such as giant cell tumor, aneurysmal bone cyst, chondromyxoid fibroma, and osteoblastoma require a more aggressive surgical technique. This usually entails several steps which together allow the surgeon to control the tumor bed and result in a high likelihood of local control.
The steps for effective intralesional surgery are as follows:
- Extensive soft tissue exposure
- Large bone window to completely expose all surfaces of the underlying cavity
- Wide resection of any area of soft tissue extension
- Complete curettage of all gross tumor tissue in the cavity
- Burring the perimeter of the bony cavity to extend the curettage beyond all visible areas of tumor extension
- Pulsatile lavage to expose clean surfaces of adjacent bone
- Many other adjuncts are also possible such as electrocautery, argon beam coagulation, cryotherapy, phenol, laser, etc.
- Reconstruction with bone cement or bone graft with or without internal fixation as needed for bony stability and joint surface support
The treatment of sarcomas of bone and soft tissue may be broadly summarized as follows:
Radio-resistant low-grade tumors
Surgery alone
- Chondrosarcoma
- Chordoma
- Adamantinoma
Radio-sensitive low-grade tumors
Surgery plus radiation
- Low-grade soft tissue sarcomas
High-grade bone sarcomas
Surgery plus chemotherapy
- Osteosarcoma
- Ewing sarcoma
- Other high-grade bone sarcomas
High-grade soft tissue sarcomas
Surgery plus radiation with possible chemotherapy
- High-grade soft tissue sarcomas
There are four possible margins that a tumor resection can provide, namely intralesional, marginal, wide, and radical. These margins apply to both local tumor resections and amputations.
An intralesional margin is created when the surgery comes through the lesion.
A marginal margin occurs when the surgery comes across the outer margin of the tumor.
A wide resection occurs when there is some normal tissue between the tumor and the plane of resection.
A radical margin occurs when the surgery does not enter the compartment housing the tumor.
For example, simple lipomas have a very low recurrence rate following simple excision through the outer margin of the tumor thereby creating a marginal resection.
Most current sarcoma surgery utilizes a wide margin, again with some normal tissue completely between the tumor and the plane of resection, and this is applicable to both bone and soft tissue malignancies.
Examples of a radical margin would be complete resection of the anterior compartment of the thigh for an anterior compartment soft tissue sarcoma or hip disarticulation for an osteosarcoma of the distal femur.
Low-grade bone sarcomas such as chondrosarcoma and adamantinoma respond primarily to surgery so that this is the only modality commonly utilized in their treatment. High-grade bone sarcomas such as osteosarcoma and Ewing sarcoma respond well to chemotherapy, and this is therefore a consistent part of these treatment protocols.
Other high-grade bone sarcomas such as undifferentiated pleomorphic sarcoma in bone, high-grade chondrosarcoma, and dedifferentiated chondrosarcoma present a challenge due to their significant metastatic rate. While there is a lack of data demonstrating the effectiveness of chemotherapy for these lesions, chemotherapy is occasionally utilized to both increase resectability and decrease the progression of systemic spread.
Radiation is still a possible local treatment for Ewing sarcoma but surgery is preferred when feasible due to the potential for post-radiation morbidity and malignant transformation. Despite this, radiation is still utilized and remains reasonable in cases where resection carries unacceptable morbidity or when surgical margins are closer than desired.
Low-grade soft tissue sarcomas respond well to a combination of wide resection surgery and local radiation. The radiation can be given either preoperatively or postoperatively. In either case, there is no difference in local control if the treatments are well planned.
The major advantage to preoperative radiation is that the presence of the lesion allows the radiation oncologist to conform the treatment field to the tumor in three dimensions which will usually treat a smaller field size than in cases where the lesion has been removed previously.
Radiation also has beneficial physical effects on the local tumor which will commonly decrease in size and vascularity as well as increase in firmness, thereby greatly facilitating resection.
The disadvantage of preoperative treatment is that it necessitates operating through tissues that have been damaged by receiving usually 50 gray (5000 rads) of radiation. This carries a 20% or greater risk of major wound complications in most series.
High-grade soft tissue sarcomas still present a major challenge to the oncology team. Local control can frequently be accomplished with radiation and wide resection as with the low-grade malignant lesions.
Ideally, the high-grade lesions should also receive systemic treatment due to the higher rate of metastasis associated with high-grade histology. While these patients are commonly treated with protocols which include multidrug chemotherapy, the results of this treatment in terms of improved survival are not as dramatic as we would hope.
However, some high-grade soft tissue sarcomas such as synovial sarcoma do show a significant response to systemic chemotherapy. Chemotherapy for high-grade soft tissue sarcomas as a group continues to be a controversial topic and one where much research is needed.
Hopefully, new findings regarding the molecular and genetic bases of these diseases will spawn new drug treatments for all types of sarcomas and further improve the survival of these patients.