Maryamrmpatel@yahoo.com Introduction: 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 centers in South Africa still mostly make use of ^99mTc-MDP bone scintigraphy in the staging work-up of these patients, likely due to the relatively low cost, availability, and physician familiarity with this imaging modality. ^99mTc-MDP bone scintigraphy is highly sensitive in detecting osteoblastic skeletal metastases secondary to osteoblastic response to bone destruction by cancer cells. ¹⁸F-FDG PET/CT scans assist in detecting skeletal metastases by the tumor's high glucose metabolism and are more sensitive in detecting lytic lesions and purely marrow involvement. Additional soft tissue involvement can also be detected using this imaging modality. However, it is less sensitive than ^99mTc-MDP bone scintigraphy in detecting osteoblastic lesions. The purpose of this cross-sectional study is to compare the detection of suspected metastatic skeletal lesions in both ^99mTc-MDP bone scintigraphy and ¹⁸F-FDG PET/CT scans as well as its impact on management. Methods: Forty-six (46) breast cancer patients (1 male and 45 females) with an age range of 26 to 78 years (mean, 52 years) underwent a ¹⁸F-FDG PET/CT scan and a ^99mTc-MDP bone scintigraphy performed within 31 days between January 2017 and March 2023. Comparison was done 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 ^99mTc-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 ^99mTc-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 ^99mTc-MDP bone scintigraphy and negative on ¹⁸F-FDG PET/CT scan which resulted in change in management. This patient had triple positive IDC. With regards to tumor 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-FDG PET/CT 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 ^99mTc-MDP bone scintigraphy, except in one case with purely osteoblastic skeletal lesions. Article published online: 25 May 2023 © 2023. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting unrestricted use, distribution, and reproduction so long as the original work is properly cited. (https://creativecommons.org/licenses/by/4.0/) Thieme Medical and Scientific Publishers Pvt. Ltd. A-12, 2nd Floor, Sector 2, Noida-201301 UP, India

Background: Breast cancer (BC) frequently disseminates to bone. Technetium 99m methylene diphosphonate bone scintigraphy (^99m Tc‐MDP bone scintigraphy) is utilized in the staging work‐up. In detecting lytic bone lesions, bone marrow and soft tissue metastases, 2‐deoxy‐2[fluorine 18] fluoro‐D‐glucose positron emission tomography/computed tomography scan (¹⁸F‐FDG PET/CT scans) is superior. We compared bone metastases (BM) detection in both imaging modalities, and its impact on patient management. Method: One hundred BC patients underwent ¹⁸F‐FDG PET/CT scan, and ^99m Tc‐MDP bone scintigraphy performed within a maximum of six weeks of each other, between January 2017 and September 2024. Comparison based on lesion‐by‐lesion analysis. Changes in stage and management recorded. Results: The median patient age was 55 years. ^99m Tc‐MDP bone scintigraphy detected 243 BM and ¹⁸F‐FDG PET/CT scans detected 421 BM. Stage and management upgrades, secondary to detected BM, were seen in 22 patients for each imaging modality. ¹⁸F‐FDG PET/CT scans additionally detected 5 patients with unsuspected, isolated soft tissue metastases, all resulting in stage and management change (p<0.001). Conclusion: Both ¹⁸F‐FDG PET/CT scan and ^99m Tc‐MDP bone scintigraphy demonstrated the ability to detect BM in an equivalent number of patients. However, ¹⁸F‐FDG PET/CT scan proved superior in overall metastatic assessment, particularly in identifying additional BM and concomitant soft tissue metastases. This broader disease characterization translated into significantly higher rate of management modification compared with ^99m Tc‐MDP bone scintigraphy. Contribution: A proposed revision of current BC guidelines reflecting ¹⁸F‐FDG PET/CT scan’s validated diagnostic superiority, will reduce financial burden whilst improving patient management and compliance.