Oncogene pathway activation in mammary tumors dictates FDG-PET uptake

Imaging of Tumor Metabolism Using Positron Emission Tomography (PET)

Molecular imaging employing PET/CT enables in vivo visualization, characterization, and measurement of biologic processes in tumors at a molecular and cellular level. Using specific metabolic tracers, information about the integrated function of multiple transporters and enzymes involved in tumor metabolic pathways can be depicted, and the tracers can be directly applied as biomarkers of tumor biology. In this review, we discuss the role of F-18-fluorodeoxyglucose (FDG) as an in vivo glycolytic marker which reflects alterations of glucose metabolism in cancer cells. This functional molecular imaging technique offers a complementary approach to anatomic imaging such as computed tomography (CT) and magnetic resonance imaging (MRI) and has found widespread application as a diagnostic modality in oncology to monitor tumor biology, optimize the therapeutic management, and guide patient care. Moreover, emerging methods for PET imaging of further biologic processes relevant to cancer are reviewed, with a focus on tumor hypoxia and aberrant tumor perfusion. Hypoxic tumors are associated with poor disease control and increased resistance to cytotoxic and radiation treatment. In vivo imaging of hypoxia, perfusion, and mismatch of metabolism and perfusion has the potential to identify specific features of tumor microenvironment associated with poor treatment outcome and, thus, contribute to personalized treatment approaches.

Do clinical, histological or immunohistochemical primary tumour characteristics translate into different (18)F-FDG PET/CT volumetric and heterogeneity features in stage II/III breast cancer?

PURPOSE

The aim of this retrospective study was to determine if some features of baseline (18)F-FDG PET images, including volume and heterogeneity, reflect clinical, histological or immunohistochemical characteristics in patients with stage II or III breast cancer (BC).

METHODS

Included in the present retrospective analysis were 171 prospectively recruited patients with stage II/III BC treated consecutively at Saint-Louis hospital. Primary tumour volumes were semiautomatically delineated on pretreatment (18)F-FDG PET images. The parameters extracted included SUVmax, SUVmean, metabolically active tumour volume (MATV), total lesion glycolysis (TLG) and heterogeneity quantified using the area under the curve of the cumulative histogram and textural features. Associations between clinical/histopathological characteristics and (18)F-FDG PET features were assessed using one-way analysis of variance. Areas under the ROC curves (AUC) were used to quantify the discriminative power of the features significantly associated with clinical/histopathological characteristics.

RESULTS

T3 tumours (>5 cm) exhibited higher textural heterogeneity in (18)F-FDG uptake than T2 tumours (AUC <0.75), whereas there were no significant differences in SUVmax and SUVmean. Invasive ductal carcinoma showed higher SUVmax values than invasive lobular carcinoma (p = 0.008) but MATV, TLG and textural features were not discriminative. Grade 3 tumours had higher FDG uptake (AUC 0.779 for SUVmax and 0.694 for TLG), and exhibited slightly higher regional heterogeneity (AUC 0.624). Hormone receptor-negative tumours had higher SUV values than oestrogen receptor-positive (ER-positive) and progesterone receptor-positive tumours, while heterogeneity patterns showed only low-level variation according to hormone receptor expression. HER-2 status was not associated with any of the image features. Finally, SUVmax, SUVmean and TLG significantly differed among the three phenotype subgroups (HER2-positive, triple-negative and ER-positive/HER2-negative BCs), but MATV and heterogeneity metrics were not discriminative.

CONCLUSION

SUV parameters, MATV and textural features showed limited correlations with clinical and histopathological features. The three main BC subgroups differed in terms of SUVs and TLG but not in terms of MATV and heterogeneity. None of the PET-derived metrics offered high discriminative power.

Metabolic tumor burden is associated with major oncogenomic alterations and serum tumor markers in patients with resected pancreatic cancer

Pancreatic cancer is an aggressive and lethal disease with an overall 5-year survival rate of only 5%. Studies have demonstrated the ability of (18)F-fludrodeoxyglucose ((18)F-FDG) positron emission tomography/computed tomography (PET/CT) to measure the metabolic tumor burden in patients with various tumors, including pancreatic cancer. In a previous study, we investigated the predictive significance of the metabolic tumor burden in terms of the metabolic tumor volume (MTV) and total lesion glycolysis (TLG). In this study, we analyzed the correlation between metabolic tumor burden and the status of the KRAS, TP53, CDKN2A/p16, and SMAD4/DPC4 genes. Our results showed that the metabolic tumor burden was associated with oncogenomic alterations that reflected the abnormal expression of carbohydrate metabolic enzymes (GLUT1, ALDOA and FBP1). We also identified a linear correlation between serum tumor markers and the metabolic tumor burden. To estimate the metabolic tumor burden when (18)F-FDG PET/CT is not available, we used the linear regression models to establish equations for MTV and TLG using CA19-9 and CA125 as independent variables. Our results suggest that the metabolic tumor burden, as evaluated by (18)F-FDG PET/CT or estimated by serum tumor markers, may be suitable for monitoring treatment response and disease progression of pancreatic cancer. Further research is needed to better understand why pancreatic cancer patients with abnormal expressions of TP53, CDKN2A/p16, and SMAD4/DPC4 get high metabolic tumor burden.