A visual inspection of whole mount Carmine Alum or haematoxylin-eosin-stained glands did not reveal obvious differences in the amount of tumourous tissue between the PyMT and PyMT;Col15a1−/− mice at 6, 9, 11 or 13 weeks of age (Figure 1D,E, some data not shown), most likely because of the substantial variation in the amount of tumourous tissue in different glands in both genotypes. Here, COL15A1 is linked to neoplasm.