The safety and clinical impact of ultra-low-dose FDG-PET imaging in pregnancy-associated breast cancer: the experience of a major tertiary oncology referral centre in the UK and suggested imaging protocol.

Background: Pregnancy-associated breast cancer (PABC) is a complex condition affecting 1 in 3000 pregnancies worldwide. While clinical management has improved, the optimal staging approach for PABC remains uncertain. 18F-fluorodeoxyglucose PET (FDG-PET) imaging is a standard diagnostic tool for many cancers. However, its use in PABC staging is controversial due to potential radiation risks to the foetus.

Methods: This retrospective case series analysed clinical data from six patients with high-risk PABC who underwent FDG-PET imaging for staging between 2022 and 2023. FDG-PET was based on locally implemented ultra-low-dose imaging protocols. The radiation doses to the foetus were dosimetrically estimated based on dose-per-unit activity values and correlated with postpartum neonatal outcomes.

Results: The median foetal radiation dose was 0.975 mGy (range 0.6-1.5 mGy) and was below the threshold for deterministic toxicities. PET imaging upstaged nodal involvement in 33% of patients and influenced treatment decisions. FDG-PET imaging provided valuable staging information in all cases. No adverse foetal effects were observed.

Conclusion: Ultra-low-dose FDG-PET imaging is a valuable tool providing accurate staging information to guide treatment decisions. The low radiation dose associated with this technique makes it a clinically acceptable modality for cancer staging in pregnant women. A larger case series is needed to precisely quantify foetal radiation doses and assess long-term safety.