Abstract P3-18-01: Assessmentof DCISionRT for guiding radiotherapy of DCIS in Sweden
Authors: Wärrnberg Fredrik , Wadsten Charlotta , Karakatsanis Andrea , Bagge Roger Olofsson , Holmberg Erik , Karlsson Per , Lindman Henrik , Whitworth Pat W , Sawyer Elinor , Shah Chirag , Shivers Steve , Vicini Frank , Mann Bruce G , Bremer Troy 
Published: March 2022

Background: Radiotherapy (RT) after breast conserving surgery (BCS) for ductal carcinoma in situ (DCIS) reduces the relative ipsilateral breast event (IBE) risk by 50%. The DCISionRT® test estimates IBE risk in DCIS women treated with BCS, and RT benefit. The test has been validated in five cohorts, including the SweDCIS randomized trial. Swedish national guidelines define low-risk DCIS using clinicopathology criteria. Methods: We determined the number of women irradiated per IBE prevented and treatment-costs based on 10-year outcomes from the SweDCIS trial. Four strategies were compared: no RT (Strategy 1); RT for all (Strategy 2), RT for DCISionRT Elevated Risk only (Strategy 3); Swedish DCIS Guidelines, omit RT for low-risk (Strategy 4). In SweDCIS, women were randomised to RT or not after BCS, 1988-2000 (n=1046). Data for DCISionRT biomarkers (PR, HER2, Ki67, FOXA1, p16/INK4A, SIAH2, COX2) and clinical factors (age, tumor size, margin, palpability) were available for 504 women with negative margins. A decision score (DS, 0-10) was reported. The associations between Low (DS≤3) and Elevated Risk (DS&gt;3) groups, and 10-year recurrences, and RT effect were assessed. Algorithms for mean treatment costs depending on adjuvant RT and type of recurrence, including secondary surgery, reconstruction, RT, and chemotherapy were based on data from 74 women with recurrence (41 invasive/33 in situ). Costs were based on diagnostic related grouping (DRG) in Sweden, 2020 and transformed to US dollar($). Results: In the SweDCIS validation of DCISionRT, the test divided women into Elevated (52%) and Low Risk (48%) groups. In the Elevated Risk group, RT decreased 10-year relative total and invasive recurrence rates, HR 0.32 (95%CI 0.17-0.58) and 0.24 (0.08-0.74), respectively with absolute decrease of 15.5% (5.9-25.0%) and 9.3% (2.0-16.5%). In the Low Risk group, the relative RT benefit was lower, HR 0.53 (0.28-1.02) and 0.84 (0.30-2.31), with decrease of 5.7% (-0.8-12.2%) and 1.2% (-5.7-8.2%). Invasive and in situ recurrences had an average treatment cost of $21,228 and $19,777, respectively. Treatment of recurrences after initial RT was $983 less expensive. RT-cost was $4,899. Strategy 1: For every 1000 women, 186 develop an IBE within 10-years after BCS without RT, with a treatment-cost in Sweden of $3,752,099. Strategy 2: Treating all women with RT prevents 108 IBE with treatment-costs of $6,467,113. Strategy 3: Treating women at DS Elevated Risk with RT prevents 81 IBE and 480 women are spared RT, with treatment-costs of $4,681,394. The cost of the test is not included. Strategy 4: Using Swedish Guidelines, prevents 100 recurrences and 870 receives RT with treatment-costs of $5,998,002. Compared to Strategy 1, Strategies 2, 3 and 4 decrease IBEs with increased treatment-costs. Treatment-costs increased $25,139/IBE prevented by Strategy 2, $11,473/IBE prevented by Strategy 3, and $26,115/IBE prevented by Strategy 4. The number of women irradiated per IBE prevented were 9.3, 6.4, and 10.1 for strategies 2, 3 and 4, respectively, relative to Strategy 1. Conclusion Strategy 1 (to omit RT) had the lowest treatment-costs and the highest number of recurrences. Strategy 3, using DCISionRT had the lowest number irradiated per IBE prevented at the lowest treatment-cost per IBE prevented.

Table 1.DCIS BCS +/-RTRT%Recurrences per 1000 womenCost including RT and treatment of recurrence per 1000BCS RT(-)0%186$3,752,099BCS RT(+)100%78$6,467,113DCISionRT52%105$4,681,394Swedish Guidelines*87%86$5,998,002*Low-risk criteria from modified Swedish national guidelines NG 1–2, &lt;1.5 cm, negative margin, and &lt;52 years (mean age for menopause)

Citation Format: Fredrik Wärrnberg, Charlotta Wadsten, Andrea Karakatsanis, Roger Olofsson Bagge, Erik Holmberg, Per Karlsson, Henrik Lindman, Pat W Whitworth, Elinor Sawyer, Chirag Shah, Steve Shivers, Frank Vicini, Bruce G Mann, Troy Bremer. Assessmentof DCISionRT for guiding radiotherapy of DCIS in Sweden [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-18-01.