Novel imaging and circulating biomarkers in hepatic malignancies
Keywords: SIRT
perfusion imaging
ctDNA

Colorectal cancer (CRC) that has metastasised to the liver has a median survival of less than 24 months unless patients have resectable disease. Liver-directed therapies target disease to improve hepatic disease-control. Selective internal radiation therapy (SIRT) exploits the arterial blood supply to the liver to deliver yttrium-90 (90Y) microspheres. Optimising radiation delivery whilst sparing normal liver is an important part of the work-up. Imaging biomarkers to determine vascularity and microcirculation may improve patient selection for liver-directed therapies. This research project studied the following imaging modalities to optimise patient selection for liver-directed therapy: perfusion computerized tomography (pCT); dynamic contrast enhanced magnetic resonance imaging (DCE MRI); T1 mapping (native and oxygen-enhanced) MRI.
Patients were recruited in three clinical trials, each exploring tissue and imaging biomarkers of potential response to therapy: FOXFIRE; PERFORM and NICOLA studies. The PERFORM trial investigated the feasibility of multi-parametric imaging to measure hepatic perfusion and generate parameter maps pre- and post-SIRT treatment through pCT and DCE MRI. The distribution and location of microspheres were described through the histopathological analysis of patients from the FOXFIRE study in patients who had hepatic resection post-SIRT. T1 mapping pre- and during high flow oxygen inhalation in the NICOLA study explored the role of this emerging technique for the characterisation of liver lesions having a hepatic resection.
The potential role of complimenting imaging biomarkers with circulating biomarkers was also explored. Circulating tumour DNA (ctDNA) was extracted at three time-points having pCT and DCE MRI after SIRT. Ion Torrent Amplicon sequencing detected multiple somatic mutations associated with CRC and the quantification of these mutations over time. This was also expanded to include patients with intrahepatic cholangiocarcinomas (ICC) and included some measurements of circulating metabolites with liquid chromatography mass spectrometry.
The PERFORM study recruited 58 patients to examine the feasibility of pCT and DCE MRI to generate perfusion parameters pre- and post-SIRT. The hypothesis was that baseline perfusion parameters reflecting high blow flow would increase delivery of SIRT microspheres and would predict for response. The second hypothesis was that a reduction in perfusion parameters would act as a biomarker for the response to the targeted delivery of 90Y, at four weeks rather than the standard imaging at 12 weeks.
The acquisition and analysis of pCT parameters was completed via 4D perfusion software. Specific parameters measured were – blood flow; blood volume; mean transit time and permeability surface area product. Pharmacokinetic modelling post DCE MRI acquisition supported the generation of Ktrans, Kep and Vep mapping. Measurement of each parameter at a range of time intervals failed to demonstrate a specific imaging predictive biomarker of response to SIRT. DCE MRI analysis did reveal parameter changes over time, although the mean values did not discriminate treatment responders from non-responders.
Quantitative T1 mapping using shortened Modified Look-Locker Inversion recovery (shMOLLI) was performed on 11 patients and explored oxygen as a non-invasive contrast agent. The feasibility of this technique for quantitative T1 mapping in malignant hepatic lesions was demonstrated for the first time and analysis of data supported the need for further research into the role of T1 mapping pre and post oxygen-enhancement for patients receiving neo-adjuvant chemotherapy.
The analysis of the resected tumour specimens from the FOXFIRE study demonstrated that the density of microspheres was highest 0-1 mm within the tumour margin. The location of microspheres also showed clustering around the endothelium. The analysis of macrophages revealed giant cell reactions around microspheres with increased numbers of tumour-associated macrophages. The results from the ctDNA revealed high concordance of KRAS status up to 1127 days from primary CRC to ctDNA results. Variant allele frequencies were measured during treatment with SIRT and detected common genes associated with CRC including APC, AKT and BRAF. The exploration of ctDNA and metabolites in four patients with ICC confirmed the presence of elevated circulating 2-hydroxyglutarate in a patient with an IDH1 mutation.
In summary, the feasibility of pCT and DCE MRI is shown, but further work is required to validate these techniques as a measure of vascularity that will predict for SIRT delivery. The findings from FOXFIRE resection analysis confirmed the changes and deposition from microsphere delivery. T1 mapping has been used for one of the first times to assist in the characterisation of suspected hepatic malignancies and suggests that the role of oxygen as a non-injectable contrast agent is worth pursuing. The addition of circulating biomarkers in helps to integrate multiple biomarkers into cancer care, pairing biology with imaging. It is likely a combined approach like this may need to be adopted in this emerging era of precision medicine.