The present study confirmed that simple carcinomas with a solid pattern are typical of tumors driven by the Neu and Ras pathways, whereas type P tumors are a feature of neoplasms arising in mice transgenic for Wnt1. That type P tumors are also found in MMTV-infected mice was expected because Wnt1 is activated in 75% of mammary carcinomas arising in C3H/HeJ mice [52], and this observation supports the validity of the pathway pathology hypothesis. This evidence concerns the gene ERBB2 and breast carcinoma.