Can localised 19F magnetic resonance spectroscopy pharmacokinetics of 5FU in colorectal metastases predict clinical response?

Background 5-Fluorouracil remains widely used in colorectal cancer treatment more than 40 years after its development. 19F magnetic resonance spectroscopy can be used in vivo to measure 5FU’s half-life and metabolism to cytotoxic fluoronucleotides. Previous studies have shown better survival associated with longer 5FU tumour half-life. This work investigated 5FU pharmacokinetics in liver metastases of colorectal cancer. Methods A total of 32 subjects with colorectal cancer undergoing 5FU treatment, 15 of whom had liver metastases, were examined in a 1.5T MRI scanner, using a large coil positioned over the liver. Non-localised spectra were acquired in 1-min blocks for 32 min after injection of a 5FU bolus. The 5FU half-life was measured in each subject, and averaged spectra were examined for the presence of fluoronucleotides. Associations with progression-free survival were assessed. Results No association was observed between 5FU half-life, tumour burden and survival. Half-lives were all shorter than those associated with improved survival in the literature. Remarkably, in the group with liver metastases, high levels of fluoronucleotides were associated with poorer survival; this counterintuitive result may be due to the higher levels of fluoronucleotides (whose level is higher in tumour tissue than in normal liver) in patients with higher tumour burdens. Conclusions It is recommended that future studies use chemical shift imaging at higher field strengths to better resolve tumour from normal liver. Non-localised spectroscopy retains prognostic potential by enabling straightforward detection of fluoronucleotides, which are present at very low concentrations distributed throughout the tissue.