Changes in Glucose Metabolism and Blood Flow Following Chemotherapy for Breast Cancer

Role of 18F-fluorodeoxyglucose positron emission tomography/computed tomography in the evaluation of breast carcinoma: Indications and pitfalls with illustrative case examples

Whole-body ¹⁸F-fluorodeoxyglucose positron emission tomography (PET) has been used extensively in the last decade for the primary staging and restaging and to assess response to therapy in these patients. We aim to discuss the diagnostic performance of PET/computed tomography in the initial staging of breast carcinoma including the locally advanced disease and to illustrate its role in restaging the disease and in the assessment of response to therapy, particularly after the neoadjuvant chemotherapy. Causes of common pitfalls during image interpretations will be also discussed.

Oncogene pathway activation in mammary tumors dictates FDG-PET uptake

Increased glucose utilization is a hallmark of human cancer that is used to image tumors clinically. In this widely used application, glucose uptake by tumors is monitored by positron emission tomography of the labeled glucose analogue 2[(18)F]fluoro-2-deoxy-D-glucose (FDG). Despite its widespread clinical use, the cellular and molecular mechanisms that determine FDG uptake--and that underlie the heterogeneity observed across cancers-remain poorly understood. In this study, we compared FDG uptake in mammary tumors driven by the Akt1, c-MYC, HER2/neu, Wnt1, or H-Ras oncogenes in genetically engineered mice, correlating it to tumor growth, cell proliferation, and expression levels of gene involved in key steps of glycolytic metabolism. We found that FDG uptake by tumors was dictated principally by the driver oncogene and was not independently associated with tumor growth or cellular proliferation. Oncogene downregulation resulted in a rapid decrease in FDG uptake, preceding effects on tumor regression, irrespective of the baseline level of uptake. FDG uptake correlated positively with expression of hexokinase-2 (HK2) and hypoxia-inducible factor-1α (HIF1α) and associated negatively with PFK-2b expression and p-AMPK. The correlation between HK2 and FDG uptake was independent of all variables tested, including the initiating oncogene, suggesting that HK2 is an independent predictor of FDG uptake. In contrast, expression of Glut1 was correlated with FDG uptake only in tumors driven by Akt or HER2/neu. Together, these results demonstrate that the oncogenic pathway activated within a tumor is a primary determinant of its FDG uptake, mediated by key glycolytic enzymes, and provide a framework to interpret effects on this key parameter in clinical imaging.

Effects of Detector Thickness on Geometric Sensitivity and Event Positioning Errors in the Rectangular PET/X Scanner

We used simulations to investigate the relationship between sensitivity and spatial resolution as a function of crystal thickness in a rectangular PET scanner intended for quantitative assessment of breast cancers. The system had two 20 × 15-cm² and two 10 × 15-cm² flat detectors forming a box, with the larger detectors separated by 4 or 8 cm. Depth-of-interaction (DOI) resolution was modeled as a function of crystal thickness based on prior measurements. Spatial resolution was evaluated independent of image reconstruction by deriving and validating a surrogate metric from list-mode data (d_FWHM). When increasing crystal thickness from 5 to 40 mm, and without using DOI information, the d_FWHM for a centered point source increased from 0.72 to 1.6 mm. Including DOI information improved d_FWHM by 12% and 27% for 5- and 40-mm-thick crystals, respectively. For a point source in the corner of the FOV, use of DOI information improved d_FWHM by 20% (5-mm crystal) and 44% (40-mm crystal). Sensitivity was 7.7% for 10-mm-thick crystals (8-cm object). Increasing crystal thickness on the smaller side detectors from 10 to 20 mm (keeping 10-mm crystals on the larger detectors) boosted sensitivity by 24% (relative) and degraded d_FWHM by only ~3%/8% with/without DOI information. The benefits of measuring DOI must be evaluated in terms of the intended clinical task of assessing tracer uptake in small lesions. Increasing crystal thickness on the smaller side detectors provides substantial sensitivity increase with minimal accompanying loss in resolution.

What's new in neoadjuvant therapy for breast cancer?

Neoadjuvant treatment of breast cancer is currently being used in patients with advanced disease as well as with increasing application in those that present with initially operable breast cancer. The current clinical benefits of the use of NAC include: NAC increases the possibility of the use of BCS, the safety of NAC is comparable with that of adjuvant chemotherapy, and pCR may be predictive of overall survival. Although there are still unresolved clinical questions regarding the use of neoadjuvant therapy in initially operable breast cancer, there appears to be equivalent survival to the standard of care. Future research should be aimed at tailoring treatment to individual patients using specific tumor characteristics that may predict response to different types of chemotherapy, molecular targeted therapy, and endocrine therapy.

Molecular probes for the in vivo imaging of cancer

Advancements in medical imaging have brought about unprecedented changes in the in vivo assessment of cancer. Positron emission tomography, single photon emission computed tomography, optical imaging, and magnetic resonance imaging are the primary tools being developed for oncologic imaging. These techniques may still be in their infancy, as recently developed chemical molecular probes for each modality have improved in vivo characterization of physiologic and molecular characteristics. Herein, we discuss advances in these imaging techniques, and focus on the major design strategies with which molecular probes are being developed.

PET and PET-CT Imaging in Treatment Monitoring of Breast Cancer

Breast cancer is one of the more responsive solid tumors with a wide range of systemic therapy options. The treatment of newly diagnosed breast cancer is primarily determined by the extent of disease and generally includes surgery, radiation, and chemotherapy. This article discusses the PET and PET-CT modalities for evaluating treatment response in breast cancer.

Current and future use of positron emission tomography (PET) in breast cancer

Positron emission tomography (PET) is a radiotracer imaging method that is increasingly used in both the clinical care of breast cancer patients and in translational breast cancer research. This review emphasizes current and future clinical applications of PET to breast cancer, and highlights some translational research using PET to elucidate the clinical biology of breast cancer. PET principles are reviewed, followed by a review of current applications of (18)F-fluorodeoxyglucose (FDG) to clinical breast cancer care. Finally we review work done with other radiopharmaceuticals beyond FDG designed to image a number of aspects of breast cancer biology, emphasizing those most likely to enter clinical trials in the near future.