Comparison between 18F-FDG and 18F-NaF PET imaging for assessing bone metastases in breast cancer patients: a literature review

[18F]NaF PET/CT imaging of response to single fraction SABR to bone metastases from breast cancer

Breast cancer commonly metastasises to the skeleton, and stereotactic ablative body radiation therapy (SABR) is an emerging treatment for oligometastatic disease. Accurately imaging bone metastases and their response to treatment is challenging. [18F]NaF-PET has a higher sensitivity and specificity than conventional bone scans for detecting breast cancer bone metastases. In this pre-defined secondary analysis of a prospective trial, we evaluated the change in [18F]NaF uptake after SABR. Patients with oligometastatic breast cancer received a single fraction of 20 Gy to up to three bone metastases. [18F]NaF-PET was acquired before and 12 months after SABR. Pre- and post-treatment [18F]NaF-PET images were registered to the treatment planning CT. The relative change in tumour SUVmax and SUVmean was quantified. The intersection of each of the radiation therapy isodose contours with a non-tumour bone was created. The change in SUVmean in sub-volumes of non-tumour bone receiving doses of 0-20 Gy was quantified. In total, 14 patients, with 17 bone metastases, were available for analysis. A total of 15 metastases exhibited a reduction in SUVmax; the median reduction was 42% and the maximum reduction 82%. An increased absolute reduction in SUVmax was observed with higher pre-treatment SUVmax. One patient exhibited increased SUVmax after treatment, which was attributed to normal peri-tumoural bone regeneration in the context of a bone metastasis. There was a median reduction of 15%-34% for non-tumour bone in each dose level.

Evaluation of Treatment Response in Patients with Breast Cancer

Breast cancer (BC) remains one of the leading causes of death among women. The management and outcome in BC are strongly influenced by a multidisciplinary approach, which includes available treatment options and different imaging modalities for accurate response assessment. Among breast imaging modalities, MR imaging is the modality of choice in evaluating response to neoadjuvant therapy, whereas F-18 Fluorodeoxyglucose positron emission tomography, conventional computed tomography (CT), and bone scan play a vital role in assessing response to therapy in metastatic BC. There is an unmet need for a standardized patient-centric approach to use different imaging methods for response assessment.

The current role of nuclear medicine in breast cancer

Breast cancer is the most common cancer in females worldwide. Nuclear medicine plays an important role in patient management, not only in initial staging, but also during follow-up. Radiopharmaceuticals to study breast cancer have been used for over 50 years, and several of these are still used in clinical practice, according to the most recent guideline recommendations.In this critical review, an overview of nuclear medicine procedures used during the last decades is presented. Current clinical indications of each of the conventional nuclear medicine and PET/CT examinations are the focus of this review, and are objectively provided. Radionuclide therapies are also referred, mainly summarising the methods to palliate metastatic bone pain. Finally, recent developments and future perspectives in the field of nuclear medicine are discussed. In this context, the promising potential of new radiopharmaceuticals not only for diagnosis, but also for therapy, and the use of quantitative imaging features as potential biomarkers, are addressed.Despite the long way nuclear medicine has gone through, it looks like it will continue to benefit clinical practice, paving the way to improve healthcare provided to patients with breast cancer.

Intra-individual comparison of 18F-sodium fluoride PET-CT and 99mTc bone scintigraphy with SPECT in patients with prostate cancer or breast cancer at high risk for skeletal metastases (MITNEC-A1): a multicentre, phase 3 trial

BACKGROUND

Detection of skeletal metastases in patients with prostate cancer or breast cancer remains a major clinical challenge. We aimed to compare the diagnostic performance of ^99mTc-methylene diphosphonate (^99mTc-MDP) single-photon emission CT (SPECT) and ¹⁸F-sodium fluoride (¹⁸F-NaF) PET-CT for the detection of osseous metastases in patients with high-risk prostate or breast cancer.

METHODS

MITNEC-A1 was a prospective, multicentre, single-cohort, phase 3 trial conducted in ten hospitals across Canada. Patients aged 18 years or older with breast or prostate cancer with a WHO performance status of 0-2 and with high risk or clinical suspicion for bone metastasis, but without previously documented bone involvement, were eligible. ¹⁸F-NaF PET-CT and ^99mTc-MDP SPECT were done within 14 days of each other for each participant. Two independent reviewers interpreted each modality without knowledge of other imaging findings. The primary endpoint was the overall accuracy of ^99mTc-MDP SPECT and ¹⁸F-NaF PET-CT scans for the detection of bone metastases in the per-protocol population. A combination of histopathological, clinical, and imaging follow-up for up to 24 months was used as the reference standard to assess the imaging results. Safety was assessed in all enrolled participants. This study is registered with ClinicalTrials.gov, NCT01930812, and is complete.

FINDINGS

Between July 11, 2014, and March 3, 2017, 290 patients were screened, 288 of whom were enrolled (64 participants with breast cancer and 224 with prostate cancer). 261 participants underwent both ¹⁸F-NaF PET-CT and ^99mTc-MDP SPECT and completed the required follow-up for statistical analysis. Median follow-up was 735 days (IQR 727-750). Based on the reference methods used, 109 (42%) of 261 patients had bone metastases. In the patient-based analysis, ¹⁸F-NaF PET-CT was more accurate than ^99mTc-MDP SPECT (84·3% [95% CI 79·9-88·7] vs 77·4% [72·3-82·5], difference 6·9% [95% CI 1·3-12·5]; p=0·016). No adverse events were reported for the 288 patients recruited.

INTERPRETATION

¹⁸F-NaF has the potential to displace ^99mTc-MDP as the bone imaging radiopharmaceutical of choice in patients with high-risk prostate or breast cancer.

FUNDING

Canadian Institutes of Health Research.

Rare Thyroid Cartilage Metastasis From Breast Cancer Visualized on 18F-NaF PET/CT

Metastatic involvement of the thyroid cartilage is rare due to the absence of vessels within the cartilaginous tissue. We present the case of a 65-year-old woman recently diagnosed with breast cancer referred for skeletal staging with F-NaF PET/CT. She was found to have multiple osteoblastic metastases along with thyroid cartilage metastasis. Rare thyroid cartilage metastasis on F-NaF PET/CT may have prognostic significance in cancer patients.