Abstract P3-05-34: CANTO-RT: Skin toxicities evaluation of a multicenter prospective cohort of irradiated patients for early-stage breast cancer
Authors: Allali Sofiane , Carton Matthieu , Sarrade Thomas , Everhard Sibille , Peigneux Karine , Guibert Phillipe , Chara-brunaud Claire , Blanchecotte Julien , Pasquier David , Racadot Severine , Bourgier Celine , Kirova Youlia M. 
Published: March 2023

Abstract
Purpose: Skin damage is the most common and most important toxicity during and after radiotherapy. Its assessment and understanding of the factors influencing its occurrence, is a major issue in the management of patients irradiated for an early breast cancer (BC).
Method: CANTO (NCT01993498) is a prospective clinical cohort study of 10 150 patients with stage I-III BC treated from 2012-2017 in 26 cancer centers. In this study, we used CANTO-RT, a sub-cohort of CANTO, including 3480 patients who received RT. We are focus on specifical skin toxicities: Erythema, fibrosis, telangectasia and skin color change (CTCAE v4.0). These toxicities were assessed at baseline 0-3-6 (M0), 12 (M12), 36 (M36) months. The RT-related variables were independent variables. Multivariable logistic regression models assessed associations between RT-related variables and skin toxicities of interest.
Results: We studied 3480 patients from 2012 to 2017. Patients had a median age of 56.8 years and a mean BMI of 26. The majority of patients had SBR grade 1-2, TNM 1-2, RH+/HER2- breast cancer. Most patients had conservative surgery and 52.7% received chemotherapy. All the patients received radiotherapy mainly normofractionated 50Gy in 25 fractions, in 3D, with a boost of 16Gy in 8fractions. The prevalence of toxicities of interest varied over time, so at M0, 41.1% of patients had erythema while 24.8% of patients had fibrosis. At M12 and M36, the prevalence of erythema decreased from 8.8% to 2.9% respectively while fibrosis remains stable from 25.1% to 22.5%. The prevalence of telangiectasia increases from 1% to 7.1% from M0 to M36. The prevalence of the skin color change decreased from 31.7% to 17.5% from M12 to M36. After adjustments, at M0 and M12, we showed a statistically significant association between the occurrence of skin erythema and obesity (OR: 1.3 p &lt; 0.003); the presence of axillary dissection (OR: 1.33 p &lt; 0.003); the type of surgery (OR: 0.71 p &lt; 0.001); the use of taxane- based chemotherapy (OR: 1.46 p &lt; 0.005) and the 3DvsIMRT irradiation technique (OR: 0.42 p &lt; 0.001). However, no radiotherapy factors were statistically related to erythema from M12. Regarding fibrosis, a statistically significant association is found, at M0, with age at diagnosis (OR: 1.43 p &lt; 0.018), obesity (OR: 1.44 p &lt; 0.001), tobacco (OR: 1.4 p &lt; 0.008), and the use of boost (OR: 1.61 p &lt; 0.001). Only obesity and the type of surgery received by the patient remained statistically significant factors at M12 and M36. Obesity and age at diagnosis represented at M12 and M36 a risk associated with the onset of telangiectasias. The skin color change is consistently correlated at M12-M36 with obesity and smoking. The use of a boost increases the skin color change at M36.
Conclusion: In this study we identified several risk factors for acute and late skin toxicity such as obesity in the occurrence of skin erythema, fibrosis or telangiectasia. The use of a boost was mainly related to the occurrence of skin color change while the use of IMRT-type technique decreased the occurrence of skin erythema. The knowledge of its predictive factors allows a personalized management of the patient by adapting our treatments and our monitoring according to these different factors.
Table 2a. Skin toxicity if interest: Erythema at M0 and M12 (multivariate analysis) Relationship between radiation therapy parameters and the occurrence of skin toxicity
Table 2b. Skin toxicity if interest: Fibrosis at M0, M12, and M36 (multivariate analysis) Evolution of skin toxicities of interest over time for a given patient (Sankey plot)
Table 3. Grade CTCAEv4 of toxicities of interest * A= erythema. B= fibrosis, C= telangiectasia, D=skin color
Citation Format: Sofiane Allali, Matthieu Carton, Thomas Sarrade, Sibille Everhard, Karine Peigneux, Phillipe Guibert, Claire Chara-brunaud, Julien Blanchecotte, David Pasquier, Severine Racadot, Celine Bourgier, Youlia M. Kirova. CANTO-RT: Skin toxicities evaluation of a multicenter prospective cohort of irradiated patients for early-stage breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-05-34.