Mammary tumorigenesis in mouse mammary tumor virus CYT-1 ERBB4 transgenic mice. Mammary tumor lesions observed in 52-week-old multiparous CYT-1 ERBB4 transgenic mice. (A) Low-magnification bright-field image (top) before whole mount analysis, and low-magnification (middle) and high-magnification (bottom) bright-field image after whole mount analysis in the same female CYT-1 mouse. (B) Low-magnification bright-field image before whole mount analysis of another age-matched female CYT-1 ERBB4 mouse (left), and tumor separated from the same mouse (right). Scale bar = 1 cm.