Clinical Database of Safe Personalized Adjuvant Breast Radiotherapy Based on Individual Radiosensitivity

Severe but also moderate toxicities after curative-intent radiotherapy (RT), such as a poor cosmetic outcome following breast cancer can have a negative impact on quality of life and a marked effect on subsequent psychological outcome. Nevertheless, current practice standards commonly prescribe radiation dose and volume without regard to individual radiosensitivity. In that context, a normal tissue radiosensitivity test that includes a rapid (72 h) radiosensitivity assay based on flow cytometric assessment of radiation-induced CD8 T-lymphocyte apoptosis (RILA) and other significant clinical parameters (multifactorial nomogram) was developed. The NovaGray Breast® test combines both a biological analysis (radio-induced lymphocyte apoptosis) and a predictive analysis, including external parameters related to the patient and her treatment. A negative predictive value (\>90%) was found in case of high RILA taken alone and a sensitivity of 80% to detect the toxicity with an initial AUC of 0.61. In addition, including significant clinical parameters, the AUC was increased to 0.69. Moreover, a prognosis model with RILA alone to predict the probability to develop a toxicity and performance of the model was increased with the inclusion of significant clinical parameters (C-Harell 0.61 \>\> 0.69). The NovaGray Breast® test is now validated after two prospective trials, one French (PHRC) and one European (Requite FP7). RILA and other factors have been confirmed to be independent factors that increase significantly the appearance of severe breast fibrosis. All these data have been merged into a nomogram allowing a predictive tool for daily clinical practice and then to customize radiotherapy techniques and indications. In the meantime, several treatment modifications have been suggested to reduce late effects after breast radiotherapy: Omission of radiotherapy has been suggested when luminal A tumor subtype is combined with clinical and pathologic factors defining a subgroup of patients with a low risk of ipsilateral breast recurrence. In this group, the benefits of radiotherapy are small \[6\]. In addition, low risk of recurrence was confirmed in randomized trials in a highly selected population. However, omitting radiotherapy and using intrinsic subtyping and clinical factors is a substantial change in care and could be driven by the risk of toxicity. Reduction of the breast irradiated volume is also a possibility that has been tested and published using IORT, brachytherapy or external beam radiotherapy. The first two techniques are reserved for trained and expert centres but showed encouraging results with low toxicity rates and recurrences. The recent experience of external partial breast irradiation (EPBI) with twice daily fractions regimen showed an increase risk of late side-effects leading to use hypofractionated EPBI (hEPBI) once daily, 5 days a week. This regimen could only be used in case of selecting patients with NovaGray Breast®test without individual risk of late effects. Hypofractionation has been adapted to breast cancer radiotherapy. Overall, all recent clinical trials showed only few late effects when hypofractionation was delivered to the whole breast (WB). Nevertheless, It has been shown in the TRANS-FAST trial a significant decrease of grade ≥2 bf+ for increasing values of RILA in the same extent than observed with conventional fractional schedules. These results reinforce the need of patients' selection using the NovaGray Breast® test.