HER2 and TP53 in human breast cancer : studies of methods and prognostic value

Abstract

Prognostic and predictive factors are needed for tailored therapy strategies, aimed at reducing breast cancer relapse and improving survival. The present arsenal of such factors is insufficient.

The aims of this thesis were to study the TP53 gene, and the human epidermal growth factor receptor 2 (HER2), also known as c-erbB-2 and HER2/neu, in human breast cancer, especially in relation to outcome after tamoxifen therapy. In order to make the best out of the biological markers prognostic and predictive values, optimal methods for their determinations are required, and this is also addressed in the thesis.

We found mutated TP53 to be associated with worse outcome after adjuvant chemotherapy (CMF), but to be of no statistically significant importance with regard to the outcome of adjuvant tamoxifen. However, in the total patient population, women with wild type TP53 tumours had better survival compared with women whose tumours were TP53 mutated. We used sequenced-based methodology for analysis of all TP53 exons, based on indications that this method is superior to immunohistochemistry (IHC) in prognostication of breast cancer relapse and survival.

The monoclonal antibody trastuzumab, directed against HER2, is one of many examples of emerging targeting therapies, of which tamoxifen was the first. We describe the first patients in Sweden who received trastuzumab on a named patient basis, all with advanced breast cancer failing on conventional therapy. The previously demonstrated efficacy and acceptable toxicity in randomised studies were confirmed in our small population-based patient cohort.

Endocrine therapy with tamoxifen, mediating both anti-oestrogen, and oestrogen-like effects, has been used for more than three decades. Subsequently, tamoxifen resistance is a problem for a large cohort of breast cancer patients. Preclinical as well as clinical studies have hypothesised HER2 to be involved in tamoxifen resistance through cross-talk signalling with the oestrogen receptor, via the mitogen activated protein kinase, extra cellular regulated kinases 1 and 2 (ERK1/2) pathway. We confirmed HER2 to be associated with worse outcome after tamoxifen therapy while, in contrast to other studies, we found that activated ERK1/2 immunohistochemical staining, prognosticate better outcome.

The increasing number of patients eligible for trastuzumab therapy requires reproducible, cost-effective, and high throughput assays for HER2 determinations. Immunohistochemistry and fluorescence in situ hybridisation are the most frequently used methods for evaluation of HER2 status. We demonstrate quantitative real-time PCR and an RNA expression-based methodology to generate high-quality HER2 assessments with equivalent, and in some aspects improved results, compared with immunohistochemistry and fluorescence in situ hybridisation/chromogenic in situ hybridisation.