MRI to assess chemoprevention in transgenic adenocarcinoma of mouse prostate (TRAMP)

Ultrasound and magnetic resonance imaging for group stratification and treatment monitoring in the transgenic adenocarcinoma of the mouse prostate model

BACKGROUND

The transgenic adenocarcinoma of the mouse prostate (TRAMP) is a widely used genetically engineered spontaneous prostate cancer model. However, both the degree of malignancy and time of cancer onset vary. While most mice display slowly progressing cancer, a subgroup develops fast-growing poorly differentiated (PD) tumors, making the model challenging to use. We investigated the feasibility of using ultrasound (US) imaging to screen for PD tumors and compared the performances of US and magnetic resonance imaging (MRI) in providing reliable measurements of disease burden.

METHODS

TRAMP mice (n = 74) were screened for PD tumors with US imaging and findings verified with MRI, or in two cases with gross pathology. PD tumor volume was estimated with US and MR imaging and the methods compared (n = 11). For non-PD mice, prostate volume was used as a marker for disease burden and estimated with US imaging, MRI, and histology (n = 11). The agreement between the measurements obtained by the various methods and the intraobserver variability (IOV) was assessed using Bland-Altman analysis.

RESULTS

US screening showed 81% sensitivity, 91% specificity, 72% positive predictive value, and 91% negative predictive value. The smallest tumor detected by US screening was 14 mm³ and had a maximum diameter of 2.6 mm. MRI had the lowest IOV for both PD tumor and prostate volume estimation. US IOV was almost as low as MRI for PD tumor volumes but was considerably higher for prostate volumes.

CONCLUSIONS

US imaging was found to be a good screening method for detecting PD tumors and estimating tumor volume in the TRAMP model. MRI had better repeatability than US, especially when estimating prostate volumes.

Diffusion-weighted MRI for early detection and characterization of prostate cancer in the transgenic adenocarcinoma of the mouse prostate model

PURPOSE

To improve early diagnosis of prostate cancer to aid clinical decision-making. Diffusion-weighted magnetic resonance imaging (DW-MRI) is sensitive to water diffusion throughout tissues, which correlates with Gleason score, a histological measure of prostate cancer aggressiveness. In this study the ability of DW-MRI to detect prostate cancer onset and development was evaluated in transgenic adenocarcinoma of the mouse prostate (TRAMP) mice.

MATERIALS AND METHODS

T2 -weighted and DW-MRI were acquired using a 7T MR scanner, 200 mm bore diameter; 10 TRAMP and 6 C57BL/6 control mice were scanned every 4 weeks from 8 weeks of age until sacrifice at 28-30 weeks. After sacrifice, the genitourinary tract was excised and sectioned for histological analysis. Histology slides registered with DW-MR images allowed for validation of DW-MR images and the apparent diffusion coefficient (ADC) as tools for cancer detection and disease stratification. An automated early assessment tool based on ADC threshold values was developed to aid cancer detection and progression monitoring.

RESULTS

The ADC differentiated between control prostate ((1.86 ± 0.20) × 10(-3) mm(2) /s) and normal TRAMP prostate ((1.38 ± 0.10) × 10(-3) mm(2) /s) (P = 0.0001), between TRAMP prostate and well-differentiated cancer ((0.93 ± 0.18) × 10(-3) mm(2) /s) (P = 0.0006), and between well-differentiated cancer and poorly differentiated cancer ((0.63 ± 0.06) × 10(-3) mm(2) /s) (P = 0.02).

CONCLUSION

DW-MRI is a tool for early detection of cancer, and discrimination between cancer stages in the TRAMP model. The incorporation of DW-MRI-based prostate cancer stratification and monitoring could increase the accuracy of preclinical trials using TRAMP mice.