Evaluation of Radiotherapy Dose in Secondary Breast Angiosarcoma: Implications for Pathogenesis

Background/Aim: Survivors of early-stage breast cancer (BC) are at an increased risk of secondary breast angiosarcoma (AS), a rare cancer predominantly involving the superficial breast. The role of radiotherapy (RT) in the pathogenesis of this secondary malignancy is not completely understood. This study set out to assess the absorbed RT dose in secondary breast AS in a retrospective cohort. Patients and Methods: A retrospective search for patients with BC diagnosed with secondary breast AS from 2008 to 2017 in the Helsinki University Hospital was performed. Based on available patient records, imaging, and pathology review, the AS volume was contoured in the treatment planning system. After recalculation of all RT plans, the absorbed RT dose at the skin surface and the maximum absorbed dose inside AS volume were calculated. Results: Ten patients with previous RT for BC were diagnosed with secondary breast AS. All ASs arose in the planning target volume of BC. Calculated RT dose at depths of 1 mm and 2 mm from the skin surface ranged from 67% to 90% and from 69% to 104 % of the prescribed dose, respectively. The maximum RT dose at the AS location varied from 86% to 117% of the prescribed dose. Conclusion: The calculated RT dose at the location of the secondary breast AS was not distinctively lower than the prescribed dose. Therefore, this secondary malignancy does not seem to develop at sites of low RT dose.