What is the fine-grained topic of the following text: Moreover, if local-regional failure is not a substantial risk, postmastectomy radiotherapy can increase overall mortality, said Dr. McGale, an investigator with the Early Breast Cancer Trialists' Collaborative Group (EBCTCG) and a statistician with the Clinical Trial Service Unit, Oxford, England. Only return the topic.
Postmastectomy radiotherapy risks and effects