Progress and Future Trends in PET/CT and PET/MRI Molecular Imaging Approaches for Breast Cancer

Abstract

Breast cancer is a major disease with high morbidity and mortality in women worldwide. Increased use of imaging biomarkers has been shown to add more information with clinical utility in the detection and evaluation of breast cancer. To date, numerous studies related to PET-based imaging in breast cancer have been published. Here, we review available studies on the clinical utility of different PET-based molecular imaging methods in breast cancer diagnosis, staging, distant-metastasis detection, therapeutic and prognostic prediction, and evaluation of therapeutic responses. For primary breast cancer, PET/MRI performed similarly to MRI but better than PET/CT. PET/CT and PET/MRI both have higher sensitivity than MRI in the detection of axillary and extra-axillary nodal metastases. For distant metastases, PET/CT has better performance in the detection of lung metastasis, while PET/MRI performs better in the liver and bone. Additionally, PET/CT is superior in terms of monitoring local recurrence. The progress in novel radiotracers and PET radiomics presents opportunities to reclassify tumors by combining their fine anatomical features with molecular characteristics and develop a beneficial pathway from bench to bedside to predict the treatment response and prognosis of breast cancer. However, further investigation is still needed before application of these modalities in clinical practice. In conclusion, PET-based imaging is not suitable for early-stage breast cancer, but it adds value in identifying regional nodal disease and distant metastases as an adjuvant to standard diagnostic imaging. Recent advances in imaging techniques would further widen the comprehensive and convergent applications of PET approaches in the clinical management of breast cancer.

Keywords: PET; PET/CT; PET/MR; breast cancer; molecular imaging.

Figure 1

The developing utility of PET-based techniques in breast cancer. The graph represents a timeline of important technological developments in PET-based techniques. The solid line represents the change in the number of PubMed clinical trial publications for PET and breast cancer per year between 1988 and 2018. The earliest models of PET/MR and PET/CT date back to 1987 and 1988, respectively. As shown in the figure, the use of PET in breast cancer has increased dramatically over the past years, benefiting from the development of commercial equipment and breast-specific imaging approaches.

Figure 2

A 50-year-old woman with carcinoma of the right breast. (A) Molybdenum target mammography shows a mass in the upper quadrant of the right breast with an irregular shape, fuzzy boundary, speculation, linear calcification, and a retracted nipple. (B) Enhanced MRI shows that the right breast mass was significantly enhanced during the arterial phase, with a high signal on (C) T2WI/FS and (D) DWI. Axial (E) CT, (F) fused image, (G) FDG-PET, and (H) MIP (maximal intensity projection) image show irregular nodules with intense uptake on the upper outer quadrant of the right breast. R, right; L, left; RCC, right craniocaudal; RMLO, right mediolateral oblique.

Figure 3

A 66-year-old woman with lymph-node metastasis of the left breast. Axial (A) CT, (B) FDG-PET, (C) fused image, and (D) MIP image show enlarged lymph nodes with intense uptake in the left axilla. The SUVmax was 3.4. R, right; L, left.