Her2

Her2 is a 185 kilodalton tyrosine kinase, a member of the human epidermal growth factor receptor family, which localizes to the cell membrane. It is encoded at 17q12-21.32.

FISH is the reference standard for assessing Her2 status but is technically difficult. The reproducibility and correlation of immunohistochemistry with FISH have been questioned. A bright field gold-facilitated autometallographic method (GOLDFISH) for detecting Her2 amplification holds promise of allowing FISH to be performed using immunohistochemical techniques1.

Immunohistochemical expression

It is overexpressed in 20-30% of female breast cancers. In 90% of cases, this is secondary to gene amplification. Overexpression has also been reported in 90% of ductal carcinoma in situ. This implies that gene amplification may be lost in association with the development of invasive malignancy.

In one study, the rate of both amplification and immunoreactivity was concordant in the invasive and intraduct components of the same tumour, with lower rates of positivity in both (the invasive ductal carcinoma and the intraduct carcinoma in the presence of invasion) by comparison with pure ductal carcinoma in situ2: