Studies and reports of lung metastasis of GCTB are
Studies and reports of lung ketone bodies of GCTB are rare because of the low incidence of lung metastasis. The biological behavior and clinical features of GCTB are difficult to predict [6,7]. Some researchers have attempted to analyze related clinical factors of lung metastasis, such as age, sex, primary tumor site, tumor stage, primary tumor treatment, and recurrence. However, the numbers of patients were small, and different results were reported among the studies. High-level evidence from large-sample data is lacking. Therefore, the present study focused on a large number of patients with lung metastasis in a single center. The purpose was to elucidate the clinical characteristics and risk factors for pulmonary metastasis of GCTB.
Materials and methods
Discussion Finch and Gleave  reported pulmonary metastasis of benign GCTB for the first time in 1926. Initial pulmonary metastases are rare, and most appear after the operation of the primary tumor. Previous studies have shown that most pulmonary metastases were found several months to 3 years postoperatively [3,11,12]. However, some metastases occurred more than 10 years postoperatively [6,7]; the longest occurred at 49 years postoperatively . Such case reports are very rare. The rate of lung metastasis from GCTB is very low, and only small samples of affected patients have been reported in the literature. Campanacci et al.  reported 280 cases of GCTB in 1987, and the lung metastasis rate among these cases was 2.1%. Dominkus et al.  reported 649 cases of GCTB, and 2.1% of them had lung metastasis. In 2010, Errani et al.  reported 349 cases of GCTB, and the lung metastasis rate was 4.0%. In our center, Sung et al.  reported that 6 of 111 patients with GCTB had pulmonary metastasis in 1982, and Niu et al.  reported that the rate of lung metastasis was 3.4% among 621 cases of GCTB in 2012. The clinical characteristics of lung metastatic lesions were analyzed in the present study. Most lesions were multiple and located in the bilateral lungs, and they were mainly distributed in the peripheral lung. These characteristics are similar to those of metastases of other malignant tumors. However, the biological behavior of pulmonary metastasis of GCTB differs from that of other tumors. In general, the vast majority of GCTB metastases progress slowly. The doubling time of GCTB lung metastasis is significantly longer than that of other tumors . The male: female sex ratio was 1.4:1.0 in the present study, which is the same as that in our database . This indicates no sex-related tendency of lung metastasis. There was also no significant difference in the age distribution between the present study and our database. A previous study  also suggested that the patient\'s age and sex as well as the characteristics of the primary lesion (such as the presence of a pathological fracture, the range of bone involvement, and the distance from the joint) were not significantly related to lung metastasis. In terms of location, 81.4% of the primary tumors in this study were located in the lower limbs and 18.6% were in the upper limbs. No significant difference was present between these results and those in our database. The proportions of tumors around the knee joint were also similar. The proximal extremities (femur and humerus) accounted for 23.2% of the tumor sites in the present study, which is 5.2% higher than that in our large-sample report. However, a significant difference was not shown. Therefore, our analysis does not indicate a correlation between lung metastasis and the distribution of the primary lesion. Errani et al.  reported a higher rate of lung metastasis in patients with primary tumors located in the proximal femur and distal radius. The small number of cases involving tumors in the proximal femur and humerus in our study may have accounted for the lack of a significant difference. We also analyzed the factors related to the metastasis time and found some positive results. The metastasis time was shortest for primary tumors located in the axial skeleton, second shortest for the upper limbs, and longest for the lower limbs. Donthineni et al.  reported that spinal GCTB had a high metastasis rate at 13.7%. In 2015, Chan et al.  also reported that a primary tumor located in the axial skeleton was a risk factor for lung metastasis. However, most of the literature does not support that the primary tumor site is associated with lung metastasis.