Estimating tumour volume in a primary orthotopic mouse model of human pancreatic cancer using rapid acquisition magnetic resonance imaging

Abstract

Pancreatic cancer has a mortality rate that closely approximates its incidence. This statistic highlights a dismal prognosis that has not improved despite decades of clinical trials. There is optimism that more sophisticated in vivo studies will better predict for clinical efficacy. This includes utilizing more relevant, orthotopic, primary xenograft models and incorporating imaging for tumour burden assessment. There has been hesitation in the routine incorporation of imaging in preclinical studies related primarily to the length and cost of imaging protocols. We hypothesized that rapid acquisition MR scans that balance efficiency with tumour visualization, could be effectively used to provide accurate and timely tumour size estimates. Mice bearing orthotopic primary pancreatic xenografts were study subjects. Animals were imaged on a 7 Tesla preclinical MR scanner, using the most rapid acquisition that provided adequate assessment of tumour size. Two different tumour volume estimates were made -one calculated from 2 dimensions obtained on imaging, and the other a software-based (MIPAV) volumetric analysis. Both were compared with tumour mass (range: 237 to 2575 mg). Although both calculated tumour volume (V=½ (LxW 2 )) and software-based volumetric analysis underestimated tumour size, they correlated well with tumour mass (correlation co-efficient 0.88 (p<0.0001) and 0.94 (p<0.0001) respectively). Our data demonstrate that rapid acquisition MR protocols can provide accurate tumour volume estimates to allow for longitudinal assessment of growth kinetics. This data has implications for the routine adoption of small animal imaging for preclinical studies using orthotopic pancreatic xenograft models.