Bone metastasis is an indicator of advanced lesions, and timely diagnosis is very important. The most widely used techniques include [18F]FDG PET/CT and CT. Bone metastases, which are immeasurable lesions, can occur in the entire body of patients with tumors. Most bone metastases occur in the axial skeleton, particularly in the spine, ribs, pelvis, femur, and skull, more than the appendicular skeleton[15]. Both have proven vital for detecting bone metastases[8]. However, no consensus has been reached regarding the best imaging test for bone metastasis detection, making it difficult for clinicians to treat [16]. Our study was a prospective study based on a medical center specializing in various bone diseases that examined patients with possible bone metastases using [18F]FDG PET/CT and CT, and performed percutaneous biopsy under CT guidance. The main finding of our study is that [18F]FDG PET/CT, compared to CT, is optimal for bone metastasis detection.
CT-guided biopsy is often recommended for the initial diagnosis of skeletal lesions and has been accepted as safe, minimally invasive, and cost-effective for diagnostic confirmation, thereby preventing the need for riskier and more invasive open surgical biopsy procedures in most patients. Previous studies have also described the success rate of CT-guided biopsy in identifying morphologically clear bone lesions to be in the range of 69–90%; however, the success rate of biopsies may be unexpectedly lower for lesions that are characterized by their metabolic information rather than by anatomic structure[7, 17]. The success rate of CT-guided biopsy is unsatisfactory. [18F]FDG PET/CT can not only target morphologically clear lesions but also metabolically active areas. PET/CT inherent quantitative nature enables accurate, reproducible measurements of radiopharmaceutical uptake in the tumour during diagnostic work-up[18]. PET/CT is also recommended as a workup for potential bone metastases (evidence-level category 2 B) by the National Comprehensive Cancer Network (NCCN) guidelines version 3.2023.
[18F]FDG PET/CT and CT, which is the optimal imaging test for bone metastases? Many studies have compared the detection efficiencies of these two imaging tests, but none of them have been prospective. In a retrospective study by Guo et al., [18F]FDG PET/CT yielded a high diagnostic success rate for evaluating bone lesions in patients[9]. The first-time diagnostic success rate of biopsy was 96.1%, which was inferior to the diagnostic success rate of the PET/CT group in our study. A retrospective study by Wu et al. reported that the overall diagnostic yield of [18F]FDG PET/CT in initial biopsies was significantly higher than that in the CT group [15]. In a study by Cornelis et al., [18F]FDG PET/CT allowed high diagnostic success of percutaneous biopsies for metabolically active lesions that are difficult to see with conventional cross-sectional imaging[19]. Other retrospective analyses have shown consistent results, the superiority of PET/CT in retrospective studies is obvious[20]. Our study compared [18F]FDG PET/CT with CT in a prospective randomized controlled trial for the first time and confirmed that [18F]FDG PET/CT has higher diagnostic accuracy and sensitivity than CT. Moreover, PET/CT's role extends beyond initial diagnosis, as it can also be used to monitor the response to treatment, assess the progression of disease, and detect recurrence. The sensitivity and specificity of PET/CT in detecting metabolic changes make it a cornerstone in the multidisciplinary approach to cancer care, particularly for those cancers known to have a high propensity for bone metastasis, such as breast, prostate, and lung cancers[21, 22].
Our study is the first prospective study to compare the clinical indicators. Considering the high cost of [18F]FDG PET/CT, CT may be more practical in this field. However, CT can lead to false-negative diagnoses and unsatisfactory pathological results that could not reach diagnoses[23]. For example, in our study, seven patients in CT group did not get diagnoses during the first pathological biopsy, compared to [18F]FDG PET/CT, only three patients failed to reach diagnoses at the first biopsy. Owing to the limitations of CT devices, if the first biopsy didn’t get the appropriate tissue,a secondary puncture must be done. The diagnostic time was prolonged due to the second biopsy and the costs went up.. PET/CT has shown significant promise for reducing the cost of cancer management by improving the accuracy of both diagnosis and staging, thereby helping to avoid expensive, futile intervetions and associated side effects. Overall, PET/CT has the potential to improve the diagnoses and reduce the cost burden over time to the healthcare system. However, the potential of PET as a tool to help in the management of cancer patients has not yet been reflected in the extent of its adoption.
Many studies have analysed the cost-effectiveness of PET/CT for preoperative staging of NSCLC and have demonstrated that the clinical use of PET/CT for staging of the disease leads to significant decreases in surgery and radiotherapy rates[24]. Cost-effectiveness analyses performed alongside the studies have established that PET/CT provides accurate preoperative staging of NSCLC and its use leads to cost savings. The systematic use of PET/CT has been shown to decrease the number of futile thoracotomies and lower the costs associated with lung cancer diagnosis and treatment [25, 26]. Similar results on head and neck squamous cell carcinoma follow-up are shown. Patients receiving PET/CT surveillance had equal survival probability, while unnecessary surgery and potential complications were avoided, and its use saved £1,492 per patient for the duration of the study[27].High uptake of SUVs represents an area with severe bone turnover. As a metabolic index, SUV can distinguish benign from malignant masses, viable from non-viable masses, or biologically aggressive from non-aggressive regions of malignant masses[17]. In [18F]FDG PET/CT, the site of SUVmax indicates the possible malignant location, where the biopsy can obtain a meaningful sample for subsequent pathological and molecular tests. Yao et al. reported an SUVmax of 5 to predict bone metastasis, and that SUVmax could be a valuable noninvasive predictor of EGFR mutations in lung adenocarcinoma[28, 29].Our study showed that SUVmax > 6.3 indicates that the bone lesion is malignant, which is higher than that reported in the literature, and can be attributed to a minority of extreme values [30]. Our data were based on a prospective study with a large sample size that used bone pathological examination as a gold standard and ALP as an additional index. Compared with previous studies, our study had the highest AUC[28, 30]. These cutoff values could be helpful when choosing the most suitable site for bone biopsy.
The goal of diagnostic imaging is to detect skeletal metastases early, whenever suspected, on the basis of clinical or laboratory findings. Bone turnover markers (BTMs) are substances released in the blood and urine that can reflect bone resorption and formation during the remodeling process and can be used to predict the risk of bone metastases. ALP, serum calcium, and phosphorus levels indicate bone osteoblast activity[12, 31]. In our prospective study, many patients did not undergo comprehensive BTM tests but only underwent routine blood tests, which merely covered the blood ALP tests and serum calcium and phosphorus levels. Univariate and multivariate logistic regression analyses were performed to determine whether these markers were associated with malignant bone metastases. Serum calcium and phosphorus levels are strongly affected by disease and diet; therefore, they are not stable indicators that can be used to diagnose bone metastases. In contrast, ALP indicates relatively stable bone metabolism.
This study has some limitations. The prospective study is single-center and the sample size was limited. Only one metabolic index and one serum index were statistically significant in assisting in diagnosing bone lesion malignancy. More significant indicators can be used for prediction.