Abstract PS11-16: Rare patients in routine care: Treatment and outcome in advanced invasive lobular breast cancer in the prospective German research platform OPAL

Introduction Invasive lobular breast cancer (ILC) is with 5-10% the second most common histologic type of invasive breast cancer after invasive ductal breast cancer (IDC). ILC differs from IDC, for example in its metastatic pattern. However, guidelines do not provide special treatment recommendations for this subtype and specific clinical studies are rare. Here we present prospective data on characteristics, treatment and outcome of patients (pts) with advanced ILC in routine care in Germany. Methods The Tumor Registry Breast Cancer (TMK) has prospectively documented data of pts with breast cancer by oncologists in Germany since 2007. Since 2017 OPAL continues the TMK work with representation of all specialists (medical and gynecologic oncologists) treating advanced breast cancer (ABC). Both projects are prospective, observational, open, longitudinal multicenter cohort studies (clinical registries). Pts at the start of their treatment can be included after signing informed consent. Together over 7500 pts (4250 with ABC) will be recruited from over 150 sites in Germany. There is no treatment specification. Details on all (sequential) treatments, patient and tumor characteristics, clinical and patient-reported outcomes are documented. Follow-Up is until death or up to 5 years. Here, data as of March, 31st 2020 are presented. Results Pts with advanced ILC (n=372) were older at start of first-line treatment (median 68 vs. 63 years) while ECOG performance status (ECOG 0 25% vs 29%) and Charlson Comorbidity Index (CCI 0: 82% vs 84%) were similar compared to pts with IDC (n=1745). The lobular tumor was more often hormone receptor (HR) positive (87% vs 74%) and less often HER2 positive (14% vs 27%). The percentage of primary metastatic disease (M1) was 34% in both groups, while grade at diagnosis was more frequently G1/2 in the ILC group (73% vs 51%). The metastatic pattern was more often non-visceral only for the ILC group (26% vs 19%), and metastases were found more often in bone (52% vs 42%) and peritoneum (9% vs 2%) and less often in liver (20% vs 25%) and lung (7% vs 25%). Overall, pts with ILC were treated more often with endocrine therapy (ET) +/- CDK4/6-inhibitors (CDK4/6i) than pts with IDC (52% vs 33%), yet, ILC is more often HR-positive than IDC. Of pts receiving chemotherapy (CT) 53% of ILC and 56% of IDC tumors were treated with taxanes as first-line treatment. 20% of ILC vs. 24% of IDC tumors received a combination-CT. First-line treatment strategy was analyzed for the HR-positive, HER2-negative subgroup. From 2007-16 pts with ILC received more often ET (ILC (n=162) 54% vs IDC (n=696) 44%), while IDC were more often treated with CT first-line. Since approval of CDK4/6i, distribution of treatment strategies has been quite similar (ILC (n=123): CDK4/6i: 76%, ET: 15%, CT: 10% and IDC (n=311): CDK4/6i: 72%, ET: 12%, CT: 15%). Overall survival (OS) from start of first-line treatment was estimated for all pts recruited by 2016 (follow-up of at least 3 years). Median OS was comparable: ILC (n=224) 30.6 months (68% events, 95%-CI 26.1 - 36.9 months) and IDC (n=1217) 34.1 months (60% events, 95%-CI 30.6 - 38.4 months). For the HR-positive, HER2-negative subgroup, OS was also similar. A multivariate regression analysis on factors affecting OS will be presented. Conclusion Registries, like TMK/OPAL, can provide data on rare tumor subtypes. We show that ABC with an invasive lobular histology differs in receptor status (more often HR-positive) and metastatic pattern (e.g. more often non-visceral) from the invasive ductal subtype. Nevertheless, treatment strategies for first-line treatment are similar and median OS is comparable despite ILC pts being markedly older. Future research should focus on identifying pts who could benefit from personalized treatment approaches including tumor subtype as a factor to consider. Citation Format: Marc Thill, Mark-Oliver Zahn, Anja Welt, Elmar Stickeler, Arnd Nusch, Thomas Fietz, Jacqueline Rauh, Natalie Wetzel, Lisa Kruggel, Martina Janicke, Norbert Marschner, Nadia Harbeck, Achim Wockel, Thomas Decker, OPAL study group. Rare patients in routine care: Treatment and outcome in advanced invasive lobular breast cancer in the prospective German research platform OPAL [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 PS11-16.