A 44-kDa glycoprotein, later to be classified as an HRG, was isolated and cloned from RAS-transformed rat fibroblasts in 1992.[3] The protein named Neu differentiation factor induced phosphorylation of p185neu (later called HER2/neu) and differentiation of human breast cancer cells.[3] Almost concomitantly, another group purified and cloned a 45-kDa protein from a human breast cell line that induced phosphorylation of p185neu/HER2, which they named HRG.[4]. The gene discussed is ERBB2; the disease is breast cancer.