ShcA (SHC1) is an adapter protein that possesses an SH2 and a PTB phosphotyrosine binding motif. ShcA generally utilizes its PTB domain to engage activated receptor tyrosine kinases (RTKs), but there has not been a definitive determination of the role of this domain in tumorigenesis. To address this question, we employed a ShcA mutant (R175Q) that no longer binds phospho-tyrosine residues via its PTB domain. Here we report that transgenic expression of this mutant delays mammary tumor onset in the MMTV-PyMT mouse model of breast cancer. Paradoxically, we observed a robust increase in the growth and angiogenesis of mammary tumors expressing ShcR175Q, which displayed increased secretion of fibronectin and expression of integrin α5/β1, the principle fibronectin receptor. Sustained integrin engagement activated Src, which in turn phosphorylated pro-angiogenic RTKs, including PDGFR, FGFR and Met, leading to increased VEGF secretion from ShcR175Q-expressing breast cancer cells. We defined a ShcR175Q-dependent gene signature that could stratify breast cancer patients with a high microvessel density. This study offers the first in vivo evidence of a critical role for intracellular signaling pathways downstream of the ShcA PTB domain, which both positively and negatively regulate tumorigenesis during various stages of breast cancer progression.