112P Correlation between HER2-negative status and risk of recurrence according to PAM50 score

The prognosis of hormone receptor (HR)-positive early breast cancer (eBC) may vary according to different factors. Human Epidermal Growth Factor Receptor-2 (HER2) is one of them. HER2-low population, defined as HER2 1+ or 2+ with negative fluorescent in situ hybridization (FISH), seems to have a different prognosis than the HER2-0. We aimed to explore the impact of HER2-negative status on the risk of recurrence according to PAM50 score. We conducted a retrospective monocentric study including all eBC patients eligible for PAM50 test, according to local recommendations. We collected for each patient tumor characteristics, PAM50 score, results of risk of recurrence (ROR) at 10 years and the HER2 subtype. The primary endpoint of this study was to evaluate correlation between HER2 status (from score 0 to 2+ with negative FISH) and PAM50 score. Correlation between HER2 score, considered as ordinal, and both the PAM50 score and the PAM50 ROR was estimated by the Pearson coefficient. From October 2016 to September 2021, we included 282 patients with median age of 58 years. One-hundred ninety eight patients (70%) had HER2 score 0, 42 (15%) had score 1+ and 42 (15%) score 2+. There was no significant difference between each HER2 subgroup, except for higher estrogen and progesterone receptors discordance and higher median age for the HER2 2+ subpopulation. PAM50 score was significantly different between the 3 subgroups of HER2, with median PAM50 score of 47 [range: 1-89] for HER2 0, 50 [15-78] for HER2 1+ and 54 [8-85] for HER2 2+ (p=0.038). PAM50 ROR at 10 years significantly differs between HER2 subgroups, with 0.11 [0.02-0.39] for HER2 0, and respectively 0.14 [0.03-0.28] and 0.14 [0.04-0.44] for HER2 1+ and HER2 2+ (p = 0.013) (without significant intrinsic difference between HER2 low subgroups). PAM50 score and risk of recurrence both increased with HER2 score (Pearson r=0.15, p=0.01, and r=0.18, p=0.002, respectively). This study suggests a correlation between HER2 status and PAM50 score. Further investigations are needed to better describe HER2-low population with larger and prospective studies.