Examples of MIN progression in three different mice. (a) An example of possible mammary intraepithelial neoplasia (MIN) regression. MIN is visible at 12 weeks of age (left) beside lymph node, but cannot be found six weeks later anywhere near the lymph node. Here, only one slice is shown demonstrating absence of a lesion near the lymph node (right). (b) MIN is first detected early on at 10 weeks of age, and in this axial MR image appears in cross section. The duct grew more distended at 12 and 14 weeks, and by 16 weeks had become an invasive tumor. The tumor then continued to grow and by 20 weeks was quite large. Interestingly, at 20 weeks it appeared that new MIN had developed close to the tumor. (c) MIN has developed at 10 weeks and does not progress to invasive cancer. Field of view for all images is 3.0 × 2.0 cm, and in-plane resolution is 117 microns.