Should fluorodeoxyglucose positron emission tomography integrated with computed tomography replace methylene diphosphonate bone scintigraphy in the management of breast cancer patients with suspected skeletal metastases?

Breast cancer is the leading cause of cancer-related death in women and the fifth leading cause of mortality worldwide. Bone metastases is the most frequent site of dissemination. Prevention of morbidity from metastases to bone requires accurate, early diagnosis for preliminary staging, planning of treatment, treatment monitoring, restaging and prediction of survival in patients with breast cancer. Many centres in South Africa still mostly make use of 99m Tc-MDP bone scintigraphy in the staging work-up of these patients, likely because of the relatively low cost, availability, and physician familiarity with this imaging modality. 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) scans are more sensitive in detecting lytic lesions and purely marrow involvement. Additional soft tissue involvement can also be detected using this imaging modality. The purpose of this cross-sectional study is to compare the detection of suspected metastatic skeletal lesions in both 99m Tc-MDP bone scintigraphy and 18F-FDG PET/ CT scans as well as its impact on management. Methods: Forty-six breast cancer patients with a mean age of 52 years underwent a 18F-FDG PET/CT scan and a 99m Tc- MDP bone scintigraphy performed within 31 days between January 2017 and March 2023. Comparison was performed based on a lesion-by-lesion analysis. The results of the image interpretation were compared retrospectively. Any change in stage and management was recorded. Results: A total of 142 lesions were detected on 99m Tc-MDP bone scintigraphy and 237 lesions were detected on 18F-FDG PET/CT scans, which led to a change in management of 12 patients with 99m Tc- MDP bone scintigraphy and 17 patients with 18F-FDG PET/CT scans. Of the 46 patients, 76% (n = 35) of patients had invasive ductal carcinoma (IDC), 13% (n = 6) had invasive breast cancer no specific type 4(IBC-NST), 4.3% (n = 2) had invasive lobular cancer (ILC) and 6.5% (n = 3) of patients had missing histological results. In 1/46 (2%), an osteoblastic lesion was detected on the 99m Tc-MDP bone scintigraphy and negative on 18F-FDG PET/CT scan, which resulted in change in management. This patient had triplepositive IDC. With regard to tumour stage (T), 63% (n = 29) had T4 lesions, 17% (n = 8) had T3 lesions, 15% (n = 7) had T2 lesions and 4% (n = 2) had T1 lesions. Detailed statistical analysis to follow. Conclusion: 18F-Fluorodeoxyglucose positron emission tomography/computed tomography scans proved to be the superior modality in detecting skeletal metastases and other soft tissue distant metastases resulting in a significant number of patients having a change in management in comparison to 99m Tc-MDP bone scintigraphy. (authors)