In 1985, the HER2 oncogene was discovered by Axel Ullrich, a young scientist at Genentech. The new oncogene revealed in rat cells was called ‘neu.’ A few years later, researchers discovered that overexpression of HER2 drove the growth of breast tumors.

The human version of this gene, called HER2 (and ErbB2), is overexpressed in about 20% to 25% of breast cancers (known as HER2-positive breast cancers) and was associated with more aggressive disease and a poor prognosis.