ESTRO 2021 Abstract Book

S939

ESTRO 2021

Conclusion In Indian women receiving HFRT, RIST peaks in week 4 and a week after RT completion. Therefore, weekly follow up during treatment should be extended by one week after completion of RT.

PO-1131 Primary tumors observed in 1325 consecutive breast cancer patients treated with whole breast RT A. Fodor 1 , C. Brombin 2 , P. Mangili 3 , R. Tummineri 1 , F. Zerbetto 1 , M. Pasetti 1 , B. Longobardi 3 , P.G. Esposito 3 , R. Castriconi 3 , I. Dell'Oca 1 , C.L. Deantoni 1 , S. Broggi 3 , A.M. Deli 1 , C. Fiorino 3,4 , A. Del Vecchio 3 , M.S. Di Serio 2 , N.G. Di Muzio 1,4 1 IRCCS San Raffaele Scientific Institute, Department of Radiation Oncology, Milan, Italy; 2 Vita-Salute San Raffaele University, University Center for Statistics in the Biomedical Sciences, Milan, Italy; 3 IRCCS San Raffaele Scientific Institute, Medical Physics, Milan, Italy; 4 Vita-Salute San Raffaele University, Radiotherapy, Milan, Italy Purpose or Objective A modified definition of second primary cancer was considered to include all primary cancers, regardless of the time of onset, observed in a large cohort of 1325 consecutive early-stage breast cancer (BCA) patients (pts) treated with whole breast hypofractionated adjuvant radiotherapy(WBHRT), where BCA was the reference (primary) cancer. Materials and Methods From 02/2009-05/2017 1325 consecutive BCA pts were treated with WBHRT, without boost. Our standard protocol included 66 months (mts) of follow up and all available information was recorded. Median age of pts was 62 (interquartile range-IR-:51.14-70.53) years. Chemotherapy was prescribed in 28%, hormonal therapy in 80.3% and monoclonal antibodies in 8.3% of pts. Genetic tests were not available. Results Median follow up was 72.43(IQR: 44.63-104.13) mts. More than half of pts had a follow up longer than 66 mts and were alive. During the observation period 81% of pts did not present any other primary tumor, 16.8% of pts one other primary tumor, 2% of pts two other primary tumors, and 0.2% of pts three other primary tumors. Of the 19% of pts with another primary tumor during the observation period the majority of pts presented a previous tumor (60.6%), 6.8% a concomitant tumor, 0.4% a previous and concomitant tumor, 3.2% a previous and successive tumor and 29% a successive tumor only. Of the pts presenting a previous tumor, 9.9% had two other primary tumors and 1.3% three other primary tumors, while of the pts presenting successive primary tumors 11.1% presented two primary successive tumors. Of the 285 other primary tumors 38.95% were BCA, 15.79% digestive tumors and 12.28% gynecologic tumors. Of all pts with other primary tumor 33.5% presented a family history of BCA. One breast angiosarcoma and one skin cancer of the irradiated breast were registered. Conclusion Radiotherapy is under special observation as it concerns secondary tumors, much more than other carcinogenic treatments as chemotherapy. Often successive primitive tumors are considered secondary cancers. A simple observation of a large cohort of 1325 consecutive BCA pts with a median age of 62 years