Abstract PS1-06: High-risk breast cancer in oldest old: Exploring the effect of different treatments on outcomes

Background: Octogenarians and nonagenarians diagnosed with breast cancer have a competing risk of death from other causes and their management is frequently found to be discordant with guidelines in comparison to the younger patients, particularly with low-risk disease. There is limited information about the disease trajectory and outcomes of patients with high-risk disease. Thus, this study was conducted. Methods: This is a retrospective, population-based observational study. Women aged 80 years of age or older and diagnosed with non-metastatic, high-risk breast cancer in Alberta, Canada between January 2004 and December 2017 were identified from the Alberta Cancer Registry. High-risk disease was defined as having any of the following; T3/4, any N positive, triple negative, or Her-2 positive disease. A risk scoring system was generated based on the presence of two anatomical and one biological high-risk features to generate 3 risk levels. Patients’ characteristics (age, Charlson comorbidity index, residence, education-, and income- quintiles), disease characteristics (stage, grade, receptor status,) treatment patterns (treatment delivered, facility) and survival were determined from linkage with administrative databases (Discharge Abstract Data, National Ambulatory Care Reporting System, and Vital statistics). Treatments were stratified into; none, hormonal treatment only (HT), surgery only (S), and surgery with any adjuvant treatment (S+A). Statistical methods included chi-square and Cox regression models. Association between patient, tumor and treatment variables and survival were assessed with uni- and multivariable analysis. Primary outcome was breast cancer specific survival (BCSS) in patients stratified by different risk levels in relation to the treatment delivered. Results: 1369 patients met the inclusion criteria. The median age was 84 years (interquartile range [IQR] 82-88). After a median follow-up of 35 months (m), 873 (64%) patients had died; 405 (46%) of deaths were due to breast cancer. On multivariable analysis, patients had a lower hazard of death from cancer if they were treated with S (HR = 0.51, 95%CI: 0.34, 0.77, p = 0.001) or S+A (HR = 0.41, 95%CI: 0.28, 0.6, p < 0.001) in comparison to HT alone. Patients who did not receive any form of treatment were more likely to die from breast cancer (HR 2.14 95%CI: 1.38, 3.31, p = 0.0006). Patients who had 1 or 2 risk features had higher cancer specific and overall survival if they had S or S+A (49/31m, 92/66m median differences respectively p < .0001). Those with 3 risk features showed longer survival if they received S+A (29/25m median differences p < .0001). Conclusions and Relevance: Our findings suggest that a significant proportion of older patients with breast cancer patients with high-risk features may have increased disease-specific mortality risk. Based on a priori risk levels, and in properly selected patients, treatment options including surgery and adjuvant treatment may be associated in longer survival. Table 1 - Population and Treatment CharacteristicsVariablesCategoryTotal (N=1369)Age group80-85817 (59.7 %)86-90388 (28.3 %)91-95146 (10.7 %)>9518 (1.3 %)Charlson Comorbidity Index0453 (33.1 %)1361 (26.4 %)>=2555 (40.5 %)TNM stageI239 (17.5 %)II663 (48.4 %)III422 (30.8 %)T stageT1416 (30.4 %)T2601 (43.9 %)T3163 (11.9 %)T4169 (12.3 %)Unknown20 (1.5 %)N stageN0526 (38.4 %)N1548 (40 %)N2159 (11.6 %)N385 (6.2 %)Unknown51 (3.7 %)Receptor statusER+orPR+andHer2-1071 (78.2 %)Her2+130 (9.5 %)ER-andPR-andHer2-123 (9 %)Unknown45 (3.3 %)Risk levels1922 (67.3 %)2371 (27.1 %)376 (5.6 %)Surgery typeNo surgery215 (15.7 %)BCS364 (26.6 %)Mastectomy790 (57.7 %)Sentinel surgeryno938 (68.5 %)yes431 (31.5 %)Chemotherapyno1337 (97.7 %)yes32 (2.3 %)Radiotherapyno991 (72.4 %)yes378 (27.6 %)Hormonotherapyno659 (48.1 %)yes710 (51.9 %) Citation Format: Abdulla Al-Rashdan, Yuan Xu, Lisa Barbera, Jeffrey Cao, Winson Cheung, Antoine Bouchard-Fortier, MayLynn Quan. High-risk breast cancer in oldest old: Exploring the effect of different treatments on outcomes [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS1-06.