Inhibition of EGFR and HER2 in Tamoxifen-resistant T47D:A18/4-OHT Breast Cancer Cells

PURPOSE: Tamoxifen has been prescribed as a very effective hormonal agent not only for the treatment of breast cancer, but also for the prevention of the disease. The development of resistance to tamoxifen is one of the most important obstacles to hormonal therapy of breast cancer. HER2 or EGFR expression has been reported to be associated with the development of tamoxifen resistance. This study was performed to evaluate the effect of HER2 and EGFR inhibition on tamoxifen resistance using tamoxifen-resistant breast cancer cells (T47D:A18/4-OHT cells). METHODS: Tamoxifen-resistant T47D:A18/4-OHT cells were established by long-term treatment of 1micrometer 4-hydroxytamoxifen on T47D:A18 human breast cancer cells. The effect of HER2 and EGFR inhibition was investigated by the use of a cell proliferation assay with treatment of trastuzumab, a monoclonal antibody to the extracellular domain of the human HER2 receptor, and ZD1839, an ERFR tyrosine kinase inhibitor. RESULTS: In contrast to T47D:A18 cells, T47D:A18/4-OHT cells showed estrogen-independent proliferation and partial regulation by treatment with tamoxifen. With a single treatment of trastuzumab or ZD1839, T47D:A18/4-OHT cell growth was reduced to 77.8% (P=0.15) or 74.4% (P=0.034) respectively, as compared to untreated cells. Combinational treatment with 1 nM estradiol resulted in a further reduction of T47D:A17 cell proliferation by 83.6% (P=0.002) for trastuzumab and 77.7% (P=0.047) for ZD1839, as compared to the single treatments. CONCLUSION: Tamoxifen resistance could be partially regulated by inhibition of HER2 or EGFR in T47D:A18/4-OHT cells, especially in combination with a low dose of estradiol. This effect may provide an important clue to overcome tamoxifen resistance in the treatment of breast cancer.

Clinical Effectiveness of Diagnosis Using Immunohistochemistry and New Grade in Gastrointestinal Stromal Tumors (GISTs)

PURPOSE: Paraffin-embedded tissue samples from the gastrointestinal tract, which had been diagnosed as tumors of a mesenchymal origin, were reviewed by an immunohistochemical staining method. The prognostic significances of the immunohistochemical subtypes and anatomical locations were also investigated. GIST, as a new grading system, was compared with the pre-existing system for its useful prognostic significance. METHODS: 122 cases were evaluated and classified by immunohistochemical staining for KIT, CD34, actin, desmin, vimentin, S-100 protein and NSE. RESULTS: Positivity for both KIT and CD34 of 92.6 and 73.8%, respectively, indicated that KIT was more effective for the diagnosis of GISTs. The stomach (62.3%) and small bowel (23.7%) were most common organs of GIST. There was no difference in the prognosis between these two organs. Immunophenotypically, the uncommitted, myoid, combined and neural types were 37.7, 23.7, 20.2 and 7%, respectively. There was no significant difference in the prognosis between these types. The old grading system showed no difference between the borderline and malignant groups (P=0.14), whereas, the new grading system showed a significant difference between the intermediate and high risk groups (P=0.01). CONCLUSION: KIT is more useful for the diagnosis of GOSTs. The immunophenotypical classification and anatomical location showed no prognostic significance in GISTs. Therefore, the new grading system might be more useful than older system.