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Comparisons of patients receiving different cancer treatments reflect the effects of both treatment and patient selection. In breast cancer, however, if radiotherapy decisions are unrelated to laterality, comparisons of left-sided and right-sided cancers can demonstrate the causal effects of higher-versus-lower cardiac radiation dose. Cardiac mortality was analysed using individual patient data for 1,934,248 women with breast cancer in 22 countries. The median date of diagnosis was 1996 and the interquartile range was 1987-2002. A total of 1,018,505 women were recorded as irradiated, 223,077 as receiving chemotherapy, 317,619 as receiving endocrine therapy and 55,264 died of cardiac disease. Analyses were stratified by time since breast cancer diagnosis, age at diagnosis, calendar year of diagnosis and country. Patient-selection effects were evident for all three treatments. For radiotherapy, there was also evidence of selection according to laterality in women irradiated 1990 or later. In patients irradiated before 1990, there was no such selection and cardiac mortality was higher in left-sided than right-sided cancer (rate ratio [RR]: 1.13, 95% confidence interval 1.09-1.17). Left-versus-right cardiac mortality RRs were greater among younger women (1.46, 1.19, 1.20, 1.09 and 1.08 after cancer diagnoses at ages <40, 40-49, 50-59, 60-69 and 70+ years, 2p trend =0.003). Left-versus-right RRs also increased with time since cancer diagnosis (1.03, 1.11, 1.19 and 1.21 during 0-4, 5-14, 15-24 and 25+ years, 2p trend =0.002) while for women who also received chemotherapy, the left-versus-right RR was 1.42 (95% confidence interval 1.13-1.77), compared to 1.10 (1.05-1.16) for women who did not (2p difference = 0.03). These results show that the relative increase in cardiac mortality from cardiac exposure during breast cancer radiotherapy given in the past was greater in younger women, lasted into the third decade after exposure and was greater when chemotherapy was also given., (© 2020 The Authors. International Journal of Cancer published by John Wiley & Sons Ltd on behalf of UICC.)

Introduction: National cancer registration data were linked to the Primary Care Prescription Database (PCPD) in England. The level of endocrine therapy (ET) prescribed in women after a diagnosis of breast cancer was studied., Materials and Methods: Cancer registrations for women diagnosed with breast cancer during 1995-2015, who survived to 31st March 2015, were linked to ET prescriptions issued during April-July 2015., Results: Among 369 277 survivors of breast cancer diagnosed during 1995-2015, 37% were prescribed ET during April-July 2015. Among women whose breast cancer diagnosis was after 31st July 2010, 81% of those recorded with oestrogen receptor positive (ER+ve) disease were prescribed ET compared with only 6% of those with ER-ve disease. Younger women usually received tamoxifen and older women usually received aromatase inhibitors., Discussion: The pattern of ET use observed in these data corresponds to that expected. This provides confidence in the potential of the PCPD for epidemiological research., (Crown Copyright © 2019. Published by Elsevier Ltd. All rights reserved.)

Purpose: To compare the effect of breast cancer radiotherapy as estimated from observational data with findings from randomized trials., Materials and Methods: Rate ratios were obtained for selected end points among 13,932 women randomly assigned to receive radiotherapy or not in trials contributing to recent meta-analyses by the Early Breast Cancer Trialists' Collaborative Group. Estimates of the same quantities were derived for 393,840 women registered with breast cancer in the US SEER registries between 1973 and 2008., Results: In the randomized trials, radiotherapy after breast-conserving surgery reduced mortality from both breast cancer (rate ratio, 0.82; 95% CI, 0.75 to 0.90) and all causes (rate ratio, 0.92; 95% CI, 0.86 to 0.99). Reductions of similar magnitude were seen in the trials of radiotherapy after mastectomy in node-positive disease (rate ratios, breast cancer 0.84; 95% CI, 0.76 to 0.94; all causes, 0.89; 95% CI, 0.81 to 0.97). In the observational data, radiotherapy after breast-conserving surgery was associated with much larger mortality reductions (rate ratios, breast cancer, 0.64; 95% CI, 0.62 to 0.66; all causes, 0.63; 95% CI, 0.62 to 0.65), whereas radiotherapy after mastectomy in node-positive disease was associated with substantial increases in mortality (rate ratios, breast cancer, 1.34; 95% CI, 1.31 to 1.37; all causes, 1.23; 95% CI, 1.22 to 1.25). Detailed adjustment of the observational data for potential confounders did not reduce the divergence from the randomized data., Conclusion: This study of mortality after radiotherapy for breast cancer found strikingly divergent results between the Early Breast Cancer Trialists' Collaborative Group meta-analyses of randomized data and the SEER observational data, even when efforts had been made to remove confounding and selection biases. Nonrandomized comparisons are liable to provide misleading estimates of treatment effects. Therefore, they need careful justification every time they are used., (© 2016 by American Society of Clinical Oncology.)