In the present study, we have modulated the levels of de novo synthesized fatty acids in mammary tumors using two transgenic mouse models that either overexpress Thrsp in the mammary gland or lack Thrsp. Overexpression of Thrsp in the mammary glands of MMTV-Neu mice shortened tumor latency and increased tumor proliferation, which was associated with increased levels of MCFA (carbon chain ≤16). The gene discussed is ERBB2; the disease is breast cancer.