Breast Cancer Adjuvant Radiotherapy and Chemotherapy Sequencing: Sequential, Concomitant, or What Else? A Comprehensive Review on the Adjuvant Combinations Journey

Up to now in breast cancer (BC) treatment, adjuvant chemotherapy (A-CT) precedes adjuvant radiotherapy (A-RT). It’s beyond question that A-RT improves local control while A-CT improves the Disease Free Survival (DFS) due to the reduction of metastatic distant recurrences. Taken togheter these two approaches impact favourably on the reduction of breast cancer mortality. In the last twenty years, the adjuvant treatment of BC has evolved quickly due to a better knowledge of its molecular biology , genetic prohile and its α/β ratio 3 / 4 Gy for the tumor and normal tissues radiosensitivity. Thus new schedules with hypofractionated radiotherapy have been tested and third generation of A-CT have been introduced leading to a better survival rate but a further delay in A-RT starting, raising the question to rethink the sequencing between these two approaches. However the sequencing timing between these two approaches still remains unchanged with A-CT before A-RT as the standard of care. Many attempts have been provided in order to optimize this sequencing. This comprehensive review is a journey among randomised, retrospective and prospective studies which highlights the past, the current and the novelties on timing sequencing proposals between these two modalities to assess the state of art. Sequential, concomitant and sandwitch modalities of chemotherapy with conventional or hypofractionated RT schedules from the most important studies will be analysed in this review.