Combination of anti-estrogenic therapy with radiation in breast cancer: Simultaneous or sequential treatment?

Adjuvant radiotherapy and adjuvant endocrine therapy are commonly given to patients with invasive breast cancer or with ductal carcinoma in situ ( DCIS). Although both therapies have been well established through a number of randomized studies, little is known about a possible interaction of both treatment modalities if they are given simultaneously. A number of in vitro studies indicated that tamoxifen treatment might reduce the intrinsic radiosensitivity of MCF- 7 breast cancer cells. Conversely, estradiol treatment increased the intrinsic radiosensitivity of MCF- 7 cells. This phenomenon has not been found in clinical studies. Retrospective analyses of prospectively randomized clinical studies did not indicate an antagonistic effect of tamoxifen on the effectiveness of ionizing radiation ( XRT), since local control has been consistently higher when XRT was combined with tamoxifen, compared to treatment with XRT alone, regardless of whether tamoxifen was started simultaneously with radiotherapy or after completion of radiotherapy. Currently there are no clinical data available that would suggest an adverse effect of adjuvant tamoxifen treatment started prior to or simultaneously with radiotherapy in breast cancer or DCIS. However, since an antagonistic effect of tamoxifen and simulteneous chemotherapy has been reported recently, the issue of simultaneous versus sequential radiation and tamoxifen treatment in breast cancer should be addressed in further studies.