FDG PET for the Detection of Bone Metastases: Sensitivity, Specificity and Comparison with Other Imaging Modalities

Preparation, Optimisation, and In Vitro Evaluation of [18F]AlF-NOTA-Pamidronic Acid for Bone Imaging PET

[¹⁸F]sodium fluoride ([¹⁸F]NaF) is recognised to be superior to [⁹⁹mTc]-methyl diphosphate ([^99mTc]Tc-MDP) and 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) in bone imaging. However, there is concern that [¹⁸F]NaF uptake is not cancer-specific, leading to a higher number of false-positive interpretations. Therefore, in this work, [¹⁸F]AlF-NOTA-pamidronic acid was prepared, optimised, and tested for its in vitro uptake. NOTA-pamidronic acid was prepared by an N-Hydroxysuccinimide (NHS) ester strategy and validated by liquid chromatography-mass spectrometry analysis (LC-MS/MS). Radiolabeling of [¹⁸F]AlF-NOTA-pamidronic acid was optimised, and it was ensured that all quality control analysis requirements for the radiopharmaceuticals were met prior to the in vitro cell uptake studies. NOTA-pamidronic acid was successfully prepared and radiolabeled with ¹⁸F. The radiolabel was prepared in a 1:1 molar ratio of aluminium chloride (AlCl₃) to NOTA-pamidronic acid and heated at 100 °C for 15 min in the presence of 50% ethanol (v/v), which proved to be optimal. The preliminary in vitro results of the binding of the hydroxyapatite showed that [¹⁸F]AlF-NOTA-pamidronic acid was as sensitive as [¹⁸F]sodium fluoride ([¹⁸F]NaF). Normal human osteoblast cell lines (hFOB 1.19) and human osteosarcoma cell lines (Saos-2) were used for the in vitro cellular uptake studies. It was found that [¹⁸F]NaF was higher in both cell lines, but [¹⁸F]AlF-NOTA-pamidronic acid showed promising cellular uptake in Saos-2. The preliminary results suggest that further preclinical studies of [¹⁸F]AlF-NOTA-pamidronic acid are needed before it is transferred to clinical research.

An Approach to Undiagnosed Bone Tumors

The radiographic appearance of primary bone tumors is important for initial diagnosis and often augments histopathological analysis. The original grading system relied on the radiographic analysis of the margin of the lesions to determine tumor aggression, which often corresponds with malignant potential. The recently developed, modified Lodwick-Madewell grading system also incorporates the appearance of lesion margins on radiographs but also considers the change in margins on serial radiographs and includes a category for clinically suspected, radiographically occult, aggressive lesions. This article reviews the prior and modified grading systems, and the concepts necessary for proper interpretation of the initial appearance of bone tumors which often determines the radiologist's recommendation for biopsy or follow-up imaging.

Bone Metastases: Mechanisms of the Metastatic Process, Imaging and Therapy

The mechanisms by which tumors metastasize to bone are complex. Upon the successful establishment of metastatic deposits in the skeleton, detection of the disease becomes essential for therapeutic planning. The roles of CT, skeletal scintigraphy, SPECT/CT, MRI, PET/CT and PET/MRI will be reviewed. Therapeutic response criteria specifically designed to evaluate bone metastases (MD Anderson/MDA criteria) can guide image interpretation. Knowledge of therapeutic strategies such as systemic therapy with bisphosphonates or radiopharmaceuticals, radiation therapy, surgery, and percutaneous interventions such as vertebroplasty and radiofrequency ablation can help the radiologist produce reports that will provide maximum benefit to clinicians and patients.

The need for bone biopsies in the diagnosis of new bone lesions in patients with a known primary malignancy: A comparative review of 117 biopsy cases

Objective

This study used a clinical dataset to investigate the proportion of the newly found bone lesions in malignant patients diagnosed by biopsy as being benign, malignant but unrelated to the primary malignancy, or bone metastases of the primary malignancy. The clinical factors that might affect the correlation between bone lesions and the primary malignancy were also analyzed. It is expected to obtain some information contributing to the clinical decision-making regarding the need for biopsy of these lesions from the research results.

Methods

Data from patients with a single known malignant tumor who had undergone biopsy of newly found bone lesions at our research institution between January 2012 and December 2017 were reviewed. Based on the pathology results, included cases were divided into a bone-metastasis-of-primary-tumor group (Group 1) and a non-bone-metastasis-of-primary-tumor group (Group 2). The sex, age, diagnostic interval time between the primary malignancy and bone lesions, clinical symptoms, number of involved bones, sites of bone biopsy, and ¹⁸F-FDG PET/CT results were compared between groups.

Results

A total of 117 patients (92 in Group 1 and 25 in Group 2) were included in the study. There was no significant difference in the sex, age or diagnostic interval time between patient groups. Of all the cases, 17.9% (21/117) were identified to be benign lesions such as fibrous dysplasia (n = 2), bone tuberculosis (n = 1), simple bone cyst (n = 1), aneurysmal bone cyst (n = 1), or solitary fibrous tumor (n = 1). Meanwhile, 3.4% (4/117) were new malignancies including chondrosarcoma (n = 1), plasmacytoma (n = 1) and bone metastases unrelated to the primary malignancy (n = 2). Bone metastases pertinent to the primary tumor accounted for 78.6% (92/117) of cases. Liver (n = 18), kidney (n = 14), breast (n = 13) and lung (n = 12) were the most common cancers among cases. Cases with clinical symptoms exhibited a higher likelihood of their bone lesions being diagnosed as bone metastases of their primary malignancy than those without clinical symptoms (81.3% (87/107) vs. 50.0% (5/10)) (P = 0.021). Neither the number of bone lesions nor the biopsy sites appeared to influence whether the bone lesions were metastases of the primary malignancy or not. In PET/CT examination, the mean maximum standardized uptake values of the two groups were similar.

Conclusions

This study indicated that more than 1/5 of newly identified bone lesions in patients with a single known malignancy were not clinically associated with their primary tumors. Furthermore, 3.4% of these were newly discovered malignant bone tumors. The presence of clinical symptoms may be a significant factor affecting whether a new bone lesion is clinically linked to a patient's primary malignancy. Based on the experience from these patients, as for the newly found bone lesions, it is worthy to perform an active biopsy on those asymptomatic ones to avoid misdiagnosis and less biopsy on symptomatic ones for the sake of less cost and risks.

Radionuclide Therapy for Bone Metastases: Utility of Scintigraphy and PET Imaging for Treatment Planning

The skeleton is a common site for cancer metastases. Bone metastases are a major cause of morbidity and mortality and associated with pain, pathologic fractures, spinal cord compression, and decreased survival. Various radionuclides have been used for pain therapy. Recently, an α-emitter has been shown to improve overall survival of patients with bone metastases from castration-resistant prostate cancer and was approved as a therapeutic agent. The aim of this article is to provide an overview regarding state of the art radionuclide therapy options for bone metastases, with focus on the role of PET imaging in therapy planning.

Novel CT and scintigraphic findings of bone metastasis from invasive lobular breast cancer

INTRODUCTION

The aim of this study is to identify and describe the computed tomography and scintigraphic imaging patterns of osseous metastasis from invasive lobular breast cancer (ILC).

MATERIALS AND METHODS

CT and skeletal scintigraphy (SS) studies of 23 patients with diagnosis of ILC and osseous metastasis on their initial presentation were reviewed.

RESULTS

Osseous metastases in 14 patients (60.8%) appear as uniform small sclerotic lesions (USSL) on CT scan. The SS in these patients were interpreted as negative for metastasis (either normal or with some equivocal findings not typical for metastasis).

CONCLUSION

Osseous metastasis from ILC can have a characteristic imaging pattern on CT and SS. The pattern of USSL on CT scan with negative SS is highly suggestive of osseous metastasis from ILC.

FDG-PET/CT compared with conventional imaging in the detection of distant metastases of primary breast cancer

PURPOSE

Evidence from studies with small numbers of patients indicates that (18)F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) accurately detects distant metastases in the staging of primary breast cancer. We compared the sensitivity and specificity of PET/CT and conventional imaging (CT, ultrasonography, radiography, and skeletal scintigraphy) for the detection of distant metastases in patients with primary breast cancer.

PATIENTS AND METHODS

We performed a retrospective review that identified 225 patients with primary breast cancer seen from January 2000 to September 2009 for whom PET/CT data were available for review. Imaging findings were compared with findings on biopsy, subsequent imaging, or clinical follow-up. Sensitivity and specificity in the detection of distant metastases were calculated for PET/CT and conventional imaging. Fisher's exact tests were used to test the differences in sensitivity and specificity between PET/CT and conventional imaging.

RESULTS

The mean patient age at diagnosis was 53.4 years (range, 23-84 years). The sensitivity and specificity in the detection of distant metastases were 97.4% and 91.2%, respectively, for PET/CT and 85.9% and 67.3%, respectively, for conventional imaging. The sensitivity and specificity of PET/CT were significantly higher than those of conventional imaging (p = .009 and p < .001, respectively). Eleven cases of distant metastases detected by PET/CT were clinically occult and not evident on conventional imaging.

CONCLUSION

PET/CT has higher sensitivity and specificity than conventional imaging in the detection of distant metastases of breast cancer. A prospective study is needed to determine whether PET/CT could replace conventional imaging to detect distant metastases in patients with primary breast cancer.