Abstract P2-18-06: Value of PAM50 risk of recurrence score in patients with HR positive HER2 negative early breast cancer and intermediate risk: A single cancer center institution prospective observational study

Background: Currently, clinico-pathological characteristics (CPC) such as tumor size, lymph node status, tumor grade, proliferation, lympho-vascular invasion and percentage of cells expressing estrogen (ER) and progesterone receptors (PR) are usually considered in order to guide decisions on adjuvant systemic therapy for women with early-stage breast cancer (EBC). The indication of adjuvant chemotherapy (ACT) or not is relatively easy in women with ER+/HER2- EBC with either poor or very good CPC. However, this decision is much more difficult in those with intermediate CPC (essentially defined by grade II tumor with low PR expression and/or intermediate proliferation). The PAM50-based Prosigna risk of recurrence (ROR) is one of the multigene assays that have been evaluated and recommended for guiding treatment decision. We report here our experience on the impact of ROR in treatment decision-making in women with intermediate CPC. Patients and methods: Between March 2016 and May 2019, ROR was performed in 200 consecutive women with intermediate CPC ER+/HER2- EBC. The clinical decision (ACT or not) was prospectively recorded before and after ROR assessment and finally after the consultation with each patient. Data were summarized by frequency and percentage for categorical variables and by median and range for continuous variables. Associations between variables will be assessed using Chi-square or Fisher’s exact test for qualitative variables and the Mann-Whitney for continuous variables. All reported p-values were two-sided. For all statistical tests, differences were considered significant at the 5% level. Statistical analysis was performed using STATA v13 software. Results: Median age at diagnostic was 57 years [30-79] and 119 (59.5%) were post-menopausal. Median tumor size was 18mm [8-70mm]. Most tumors were PR+ (n=153, 76.5%), no special type (NST) carcinomas (n=172, 86%), Elston and Ellis grade II (n=183, 91.5%), with Ki67 value between 10 and 20 % (n=117, 62.6%). Lympho vascular invasion was observed in 38 tumors (19%), 124 patients were pN0 (62%), 20 pNmi (10%) and 55 pN1a (27.5%). Using the immunohistochemical (IHC)-based definition proposed by Prat et al. (JCO 2013), 90 tumors were luminal A (45%) and 110 luminal B (55%). There was 59.5% of concordance between IHC subtype classification and PAM50. ROR distribution was as follows: ROR-low (n=33; 16.5%); ROR-intermediate (n=75; 37.5%); and ROR-high (n=92; 46%). The clinical decision of modalities of adjuvant medical therapy switched after ROR assessment for 74 patients (37%): -26 patients from ACT plus endocrine therapy (ET) to ET only (13%); 9 and 17 have respectively a ROR-low or -intermediate and 23 a luminal A tumor according to PAM50, -48 patients from ET only to ACT plus ET (24%); 7 and 41 have respectively a ROR-intermediate or high and 44 a luminal B tumor. Importantly, 8 of them don’t received ACT at the issue of the consultation with the medical oncologist. Conclusion: In our experience, the use of ROR leads us more often to escalate than de-escalate adjuvant therapy, proving that the definition of the group with intermediate prognosis remains uncertain and variable according medical teams. Citation Format: Vincent Nicolai, Julia Gilhodes, Jean Louis Lacaze, Mony Ung, Eleonora De Maio, Raphaelle Duprez-Paumier, Charlotte Vaysse, Thomas Filleron, Eva Jouve, Gabrielles Selmes, Camille Franchet, Carole Massabeau, Cyprian Chira, Francoise Izar, Henri Roche, Anne Pradines, Florence Dalenc. Value of PAM50 risk of recurrence score in patients with HR positive HER2 negative early breast cancer and intermediate risk: A single cancer center institution prospective observational study [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-18-06.