Mammary glands from multiparous WapInt6sh transgenic females show persistent alveolar hyperplasia. (a) Multiple focal alveolar hyperplasias (green arrows) are visible in this carmine alum stained whole mounted mammary gland from a multiparous WapInt6sh transgenic female. LN, lymph node. Magnification 10 ×. (b) A no. 4 mammary gland from a WapInt6sh multiparous female containing one focal hyperplasia at 10 × magnification. Inset panel shows the hyperplasia at higher magnification (25 ×). This gland and the gland shown in Panel A were each taken from mice with tumors in their contralateral no. 4 mammary glands. (c) Hematoxylin and eosin-stained 5 μm section through the focal hyperplasia shown in Panel B. Well defined acinar structures are visible at 100 × magnification surrounded by significant lymphocytic infiltration (green arrows). (d) Representative multiparous WapInt6sh mammary gland showing a more uniform persistence of alveolar hyperplasia. This female had three litters, the last of which was weaned 9 months before this gland was harvested.