HER2 as a prognostic and predictive marker for breast cancer

In recent years investigators have looked at the human epidermal growth fac tor receptor-2 (HER2), which is overexpressed in 20%-30% of breast cancer p atients, with regard to its role as a prognostic and predictive factor. Alt hough many studies have suggested that HER2 overexpression may be associate d with a poor clinical outcome, other studies have not fully supported this observation. The inconsistencies between studies may be due in part to dis crepancies between different HER2 testing methods. To overcome this problem , a radioimmunohistochemical method was developed to quantitatively measure HER2 overexpression levels in breast tumor samples. The application of thi s method demonstrated that 85% of all breast tumor samples expressed HER2 a t levels greater than normal. Of these, 23% expressed HER2 at levels betwee n 45 and 480 times greater than normal, and this was associated with poor c linical outcome. The investigation of HER2 status as a predictor of respons e to therapy has also yielded many conflicting results. Overall, it appears that HER2 overexpression may correlate with resistance to hormonal therapy , sensitivity to anthracycline-based chemotherapy and resistance to CMF. Wi th the development of targeted anti-HER2 therapies, assessment of HER2 stat us will be important in stratifying patients to the most appropriate treatm ent regimens.