ABSTRACT: The lung is the most frequent site of metastasis from soft-tissue sarcomas. Due to the relative resistance of sarcoma to either chemotherapy or radiotherapy, compared to other solid tumors, surgical management of pulmonary metastases has been a pivotal therapy in this disease. With decades of experience in numerous centers, criteria for patient selection have been ascertained and documented. We review the current literature on the use of pulmonary metastasectomy in patients with soft-tissue sarcoma, as well as survival data after such treatment. Osteogenic sarcoma is not included in this discussion. [ONCOLOGY 14(6):835-841; 2000]
Soft-tissue sarcomas represent fewer than 1% of all new malignancies, and distant metastases are the most common cause of death from these mesenchymal tumors. The incidence of metastases is 5% in patients with low-grade tumors but is as high as 40% in patients with intermediate- or high-grade sarcomas of the extremity.
The most common site of distant spread of sarcomas is the lung. Thus, a new pulmonary nodule is likely to be metastatic if the primary malignancy was a sarcoma. Metastases may occur infrequently in the skin, soft tissues, liver, and, in 3% of cases, the lymph nodes.
Although no prospective, randomized trials have evaluated the efficacy of surgical resection of pulmonary metastases from soft-tissue sarcomas, multiple retrospective studies support the use of metastasectomy in selected patients. Many single-institution series report 5-year actuarial survival rates of 15% to 35% after complete resection. However, survival data are usually presented without the true “denominator,” and patients with limited disease amenable to resection are likely to have favorable tumor biology.
Recently, these single-institution results have been verified with the publication of two large multi-institutional international retrospective databases: the European Organization for Research and Treatment of Cancer (EORTC)–Soft Tissue and Bone Sarcoma Study Group and the International Registry of Lung Metastases.
In 1882, Weinlechener performed the first operation to remove two pulmonary metastases (en bloc chest wall resection) in a patient with sarcoma who subsequently died 1 day later. Kronlein successfully resected a chest wall sarcoma and its pulmonary metastasis in 1883. After 7 years, the patient died with recurrent disease.
Alexander and Haight published the first report on the feasibility of reoperation (8 months after the first operation) for secondary sarcomas to the lung in 1947. In 1965, Thomford et al advocated the surgical treatment of pulmonary metastases in highly selected patients with a variety of primary malignancies. In 1971, Martini et al reported a 5-year survival rate of 32% and a 20-year survival rate of 18% after surgical extirpation of pulmonary metastases in patients with osteogenic sarcoma.
Prior to these reports, patients with sarcoma who developed pulmonary metastases died of pulmonary disease with no 5-year survivors. These results demonstrated the safety and survival benefits of pulmonary metastasectomy in patients with sarcoma and subsequently led to the expansion of the indications for resection in soft-tissue sarcomas, as well as tumors of epithelial origin.
A prospective database from Memorial Sloan-Kettering Cancer Center outlined disease patterns in patients with soft-tissue sarcomas and pulmonary metastases. The median overall follow-up was only 9.7 months, and most patients received optimal multimodality therapy. Important data on tumor location and histology were provided.
In 18% of all patients, the pulmonary metastases presented synchronously with the primary tumor, whereas in 38% of cases, the metastases developed metachronously. Soft-tissue sarcomas of the extremity and trunk accounted for 65% of all lung metastases (Table 1). This distribution is similar to data from the Roswell Park Cancer Institute.
According to the Memorial Sloan-Kettering and EORTC databases, the frequency of histopathologic subtypes of soft-tissue sarcoma that metastasize to the lung is as follows: leiomyosarcoma (19% to 21%), malignant fibrous histiocytoma (18% to 24%), liposarcoma (12%), synovial cell sarcoma (14% to 23%), fibrosarcoma (10% to 12%), and undifferentiated sarcoma (9%).[2,9] The incidence of pulmonary metastasis correlates with the incidence of high-grade differentiation within each histologic group (Table 2). The majority (90%) of all lung metastases develop in patients whose primary tumor was high grade; 10% are of low-grade origin.
After surgical treatment of the primary soft-tissue sarcoma, patients should be followed with physical examinations and chest radiographs at 3-month intervals for the first 2 years (Figure 1). Changes in plain radiographs or physical findings warrant the performance of a chest computed tomographic (CT) scan. The frequency of follow-up assessments is predicated on the fact that approximately 80% of all recurrences occur within the first 2 years after primary resection. Moreover, there is a 10-fold likelihood that the new lung lesion is a metastatic deposit rather than a lung primary.
If there is no evidence of disease after 2 years, patients are then followed in a similar fashion every 6 months. At 5 years, yearly examinations and chest radiographs are sufficient.
When a suspicious pulmonary lesion is identified, a fine-needle biopsy may not be necessary to establish the diagnosis, especially in a high-risk patient (Figure 2). An excisional biopsy at surgical exploration is recommended. However, exploration may be negative in up to 16% of patients. Patients are eligible for metastasectomy if the following criteria are fulfilled: (1) disease at the primary site is controlled; (2) the patient has no other extrathoracic disease; (3) the patient has no significant comorbidities contraindicating a thoracotomy; (4) pulmonary function tests indicate that the patient can tolerate complete resection; (5) there is no extensive involvement of the mediastinum or chest wall; and (6) there is a reasonable likelihood that a curative resection can be performed.
At the Fox Chase Cancer Center, we further select for patients with favorable biological behavior. If the metachronous pulmonary lesion(s) has a short disease-free interval (ie, less than or equal to 6 months), a repeat CT scan 3 months later showing multiple new nodules would select out patients who would not have benefited from a resection. Patients with radiographically stable, resectable nodules on repeat scan or if the disease-free interval is greater than 6 months, indicating a tumor with a longer doubling time, are candidates for curative resection.
Preoperative bronchoscopy is performed to evaluate endobronchial involvement. The surgical objective is to perform a complete resection and remove the minimal amount of functioning lung in anticipation of future resections. For most lesions, a wedge resection is appropriate with a margin of greater than 5 mm, if possible.
A posterolateral thoracotomy is the standard approach for unilateral lesions. A median sternotomy; staged, bilateral, posterolateral thoracotomies; or a clamshell thoracotomy (bilateral anterolateral thoracotomy) is used for bilateral lesions.
Some authors advocate bilateral exploration in every instance since CT scans may underdiagnose the extent of disease by 25% to 50%. The International Registry of Lung Metastases found a 25% incidence of underestimation and a 14% incidence of overestimation. Early detection and excision have not been shown to improve survival, and multiple reexcisions are an acceptable option. With the advent of high-resolution spiral CT scans and newer biological imaging modalities, such as fluorodeoxyglucose–positron emission tomography (FDG-PET), the accuracy of diagnosis may be improved.
New Radiographic Modalities for Diagnosis: PET
PET technology utilizes special radiation-sensitive cameras, which detect radioactive isotopes that decay by positron emission. Fluorine has been commonly used in tumor localization. [18F]-2-Fluorodeoxyglucose (FDG) is a glucose analog that accumulates in cells and thus is a convenient measure of metabolism. FDG becomes phosphorylated to FDG-6-PO4, which is preferentially trapped in tumor cells. The imagery can be quantified by the actual number of positron emissions or by calculating a standardized uptake ratio, a value that is normalized for the patient’s body weight and injected dose. It is capable of detecting metastases by virtue of their metabolic differences from surrounding normal tissue.
The utility of PET has been documented with solitary pulmonary masses; it is less well studied for multiple masses. False positives commonly occur with active inflammatory or infectious lesions; false negatives occur with tumors that have relatively low metabolic activity as well as small lesions (< 1 cm) due to limited resolution. At this time, PET is being used in conjunction with CT scan or MRI as a complementary diagnostic tool.
Video-Assisted Thoracic Surgery
The utility of video-assisted thoracic surgery (VATS) is limited for several reasons. First, many lesions that can be palpated intraoperatively may be overlooked at thoracoscopy. McCormack et al identified 10 of 18 patients with positive preoperative CT scans and initial thoracoscopy who had additional lesions at thoracotomy. Second, resection of multiple secondaries may be difficult and incomplete with VATS, and the potential for port-site recurrence is a distressing complication. Also, adhesive pleuritis encountered at reoperation may render VATS technically difficult or impossible.
Lin et al reviewed the experience with VATS metastasectomy at multiple institutions between 1991 and 1998, including only six patients with metastatic sarcoma. All lesions were removed by VATS, and no thoracotomies were required. Hospitalization after VATS was reported to be 4.4 ± 2.1 days. Mean survival was 28 months for all histologic tumors combined. The incidence of locoregional recurrence was 31%, although no port-site recurrences were noted. Among the 18 patients who had a locoregional recurrence, technical failure was cited as the cause in 3 patients.