Interactions between radiation and endocrine therapy in breast cancer.

Abstract

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 have indicated that tamoxifen treatment might reduce the intrinsic radiosensitivity of MCF-7 breast cancer cells. Conversely, estradiol treatment increases the intrinsic radiosensitivity of MCF-7 cells. In one available animal study, an antagonistic effect of tamoxifen and ionizing radiation (XRT) could not be observed. Retrospective analyses of randomized clinical studies have not indicated an antagonistic effect of tamoxifen on the effectiveness of XRT, since local control has been consistently higher when XRT was combined with tamoxifen, compared with 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 simultaneous chemotherapy has been reported recently, the issue of simultaneous versus sequential radiation and tamoxifen treatment in breast cancer should be addressed in further studies.

Does Radiotherapy Have Curative Potential in Metastatic Patients? The Concept of Local Therapy in Oligometastatic Breast Cancer

“…Although some in vitro experiments [32][33][34] demonstrated a decreased sensitivity to ionizing radiation after incubation of MCF-7 cell lines with tamoxifen, an antagonistic effect of ionizing radiation and treatment with tamoxifen has not been confirmed in animal studies [35,36]. In contrast, several large randomized clinical studies [37] comparing adjuvant tamoxifen, radiation therapy and placebo, and combined radiation therapy and tamoxifen demonstrated best results [38]. Thus, the experimental endpoints of the in vitro studies may not have been relevant for the in vivo situation, and there is no clinical data for an adverse effect of combined tamoxifen and radiation.…”

Radiooncological Aspects Regarding Multimodal Primary Treatment of Breast Cancer – a Review

“…Although some experimental data suggest that tamoxifen might decrease radiation sensitivity of breast cancer cells in vitro, clinical data do not substantiate this observation [63,64]. Moderately increased risks for late pulmonary damage and subcutaneous fibrosis have been reported at least for subsets of patients [65,66].…”

Combination of Anti-Estrogenic Therapy with Radiation in Breast Cancer: Simultaneous or Sequential Treatment?

“…This block would be augmented by tamoxifen and antagonized by estrogen, since the latter would induce cell proliferation by antagonizing the G1 block. Experimental findings are summarized in table 1 and have been reviewed in detail elsewhere [1]. Most of the studies found a synergistic or additive interaction of estradiol and XRT, and an antagonistic interaction of tamoxifen and XRT.…”

“…Recent clinical studies in ductal carcinoma in situ showed a positive effect of the combined treatment with tamoxifen and XRT on local recurrence-free survival. Due to these conflicting results, clinicians are often uncertain as to how to combine both treatment modalities [1]. This review will summarize the in vitro studies on the interaction of endocrine therapy and XRT in tumor cells and in nonmalignant tissues.…”