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HER2 in Breast Cancer
How common is HER2 in breast cancer?
Several large clinical studies have shown a relationship between the frequency of HER2 overexpression/amplification and breast cancer.
| Source | N | Definition of HER2 overexpression/HER2 amplification | Percentage of tumors with HER2 overexpression/HER2 amplification |
|---|---|---|---|
| Slamon et al, Science, 198712 | 189 | Two-fold or greater amplification of HER2 gene by Southern blot | 30% |
| Paik et al, J Natl Cancer Inst, 200015 | 2034 | Definite membrane staining by IHC in any tumor cell | 29% |
| Owens et al, Clin Breast Cancer, 200416 | 16,092 (FISH) | Two-fold or greater amplification of HER2 gene by FISH | 23% |
| 116,736 (IHC) | 2+ or higher result by IHC | 20% | |
| Seshadri et al, J Clin Oncol, 199311 | 1056 | Two-fold or greater amplification of HER2 gene by slot blot | 21% |
| Andrulis et al, J Clin Oncol, 199813 | 580 | Two-fold or greater amplification of HER2 gene by Southern blot, slot blot, and/or RT-PCR | 20% |
- HER3 is frequently co-expressed with HER2 in breast cancer, as shown in tumor cell lines, mouse transgenic tumors, and human primary breast cancers17
What is the relationship between HER2 and other breast cancer tumor markers?
Interestingly, HER2 overexpression has been significantly correlated with overexpression of other tumor markers in breast cancer. These include:
- Vascular endothelial growth factor (VEGF)18
- VEGF is responsible for tumor angiogenesis, the growth of new blood vessels that supply the tumor with oxygen and nutrients18,19
- A 2004 study of 611 patients with primary breast cancer showed a significant correlation between overexpression of HER2 and 2 VEGF isoforms (P<0.001)
- The aggressive phenotype of HER2-overexpressing tumors may be due in part to VEGF
- Estrogen (ER) and progesterone receptors (PR)
- In a 1993 study (N=1056), HER2 overexpression was significantly associated with negative ER and PR status (P<0.00001 and P<0.0006, respectively)11
- Hormones such as estrogen and progesterone may suppress HER2 expression, so that hormone-receptor–positive tumors are less likely to be HER2-positive20
- This interaction may explain why many HER2-positive tumors are unresponsive to hormone therapy20