Longitudinal Studies of Angiogenesis in Hormone-Dependent Shionogi Tumors

Vessel size imaging was used to assess changes in the average vessel size of Shionogi tumors throughout the tumor growth cycle. Changes in R2 and R2* relaxivities caused by the injection of a superparamagnetic contrast agent (ferumoxtran-10) were measured using a 2.35-T animal magnetic resonance imaging system, and average vessel size index (VSI) was calculated for each stage of tumor progression: growth, regression, and relapse. Statistical analysis using Spearman rank correlation test showed no dependence between vessel size and tumor volume at any stage of the tumor growth cycle. Paired Student's t test was used to assess the statistical significance of the differences in average vessel size for the three stages of the tumor growth cycle. The average VSI for regressing tumors (15.1 ± 6.6 wm) was significantly lower than that for growing tumors (35.2 ± 25.5 μm; P < .01). Relapsing tumors also had an average VSI (45.4 ± 41.8 μm) higher than that of regressing tumors, although the difference was not statistically significant (P = .067). This study shows that VSI imaging is a viable method for the noninvasive monitoring of angiogenesis during the progression of a Shionogi tumor from androgen dependence to androgen independence.