184PDistribution of genomically defined recurrence risk in luminal A and B breast tumors defined by inmunohistochemistry: A retrospective study in Spanish population

Background: Semiquantitative inmunohistochemical (IHC) expression of progesterone receptor (PR) adds prognostic value to the current IHC-based luminal A (LA) definition, such that patients (pts) with LA (Ki67 <14% and PR > 20%) tumors can be spared from adjuvant chemotherapy (CT). Oncotype Dx® (ODX) and MammaPrint® (MP) assays have been validated as predictors of CT benefit. This study assessed the distribution of recurrence risk in LA and LB breast tumors as defined by Ki67 and PR. Methods: A retrospective analysis was performed in 889 T1-2, N0-Nmic, M0 tumors for which ODX or MP results and local pathology data were available. Ki67 was assessed by IHC (high ≥14% and low <14%). PR was assessed by semiquantitative IHC (PR low < or = 20%, high >20%). Histological grade was defined using the Nottingham grading system. Results: Median age 54 years (18-77). All pts had HER2 negative tumors. Median tumor size 15 mm (2-88). Three hundred (33.7%) tumors were classified as LA and 589 (66.3%) as LB. Grade 1 tumors were higher in LA (27%) than in LB (19%) pts (p < 0,001). CT was first recommended in 137 pts (45.7%) with LA vs. 361 pts (61.3%) with LB tumors. ODX was performed in 432 (48.6%) pts and MP in 457 (51.4%). Recurrence risk distribution varied significantly between groups (p < 0.001). ODX: among LA pts, 71.4%, 25.7% and 2.9% had low, intermediate and high recurrence risk respectively; among LB pts respective values were 46.2%, 44.2% and 9.6%. MP: among LA pts, 81.2% and 18.8% had low and high recurrence risk, respectively; among LB pts respective values were 54.2% and 45.8% (Table). After test results CT was recommended to 61 pts (20.3%) with LA vs. 268 pts (45.5%) with LB tumors.Table184PRecurrence Risk (%)LA (n = 300)LB (n = 589)ODX (n = 432)Low71.446.2Intermediate25.744.2High2.99.6MP (n = 457)Low81.254.2High18.845.8 Open table in a new tab Conclusions: There is a wide distribution of recurrence risk results between LA and LB tumors defined by Ki67 and PR which confirms the important role of gene-expression assays in adjuvant decision making. Of note about half of pts with LB tumors had low recurrence risk indicating minimal benefit from adjuvant CT. Legal entity responsible for the study: Ministry of Health of the Community of Madrid (Spain) Funding: Ministry of Health of the Community of Madrid (Spain) Disclosure: S. López-Tarruella: Advisory role: Novartis, Pfizer, Celgene. Honoraria/lecturer: Novartis, Pfizer, AstraZeneca, Celgene, Roche. I. Márquez-Rodas: Advisory role: Bristol-Myers Squibb, MSD, Novartis, Roche, Pierre Fabre, Amgen and Bioncotech. M. Martin Jimenez: Holds a patent on the predictive value of the PAM50 gene profile assay. All other authors have declared no conflicts of interest.