Characterization of N-ethyl-N-nitrosourea-induced malignant and benign breast tumors in rats by using three MR contrast agents.

A carcinogen (N-ethyl-N-nitrosourea)-induced animal tumor model was established to grow malignant and benign breast tumors. In each tumor the pharmacokinetic characteristics were measured by using three contrast agents, gadolinium-diethylene-triamine-pentaacetic acid (Gd-DTPA; <1 kD), Gadomer-17 (35 kD), and albumin-Gd-DTPA (70-90 kD). Infiltrating ductal carcinomas (IDC) with low, medium, and high Scarf-Bloom-Richardson grades and fibroadenomas (FA) were analyzed. We found that Gd-DTPA could differentiate between FA and malignant tumors, but not between malignant tumors of low and high grades. In contrast, the intermediate size agent Gadomer-17 could differentiate between high-grade and low-grade IDC, but not between low-grade IDC and FA due to their similar enhancement patterns (despite their different origins). The largest agent, albumin-Gd-DTPA, was capable of differentiating both, but the low contrast-to-noise ratio was its major technical concern. The results in this breast tumor model suggest that macromolecular agents provide useful information for differential diagnosis among IDCs of various grades, but they do not provide superior information than Gd-DTPA for differential diagnosis between IDC and FA.