ESTRO 2024 - Abstract Book

S501

Clinical - Breast

ESTRO 2024

A cutoff of 30% was used to distinguish patients into groups of “low” and “high” levels of TILs. TILs were successfully scored in 319/349 patients from the HYPO-cohort and 911/980 from the IMN2-cohort with 18-19% being categorized as having “high TILs”, respectively. In the high-risk IMN2 cohort (Figure 1), patients with ER- /“low TILs” tumors showed a significantly worse OS after RT (Hazard ratio (HR)=0.35 (95% CI: 0.21-0.58)) as compared to patients with ER- /”high TILs” with an absolute increase in OS at 10 years of 29.4% (76.7% vs. 47.3%). No significant difference in OS was found for patients with ER positive (ER+) tumors (HR=1.02 (0.68-1.55)), and the interaction test between ER-status and TILs was significant (p<0.001). A similar association between ER-status and TILs was found for DM (HR=0.36 (0.20-0.63)), where patients with ER- /”low TILs” tumors showed an absolute increase in risk of DM at 10 years of 24.1% (42.1% vs. 18.0%) as compared to ER- /”high TILs” tumors. On the contrary, TILs did not affect loco -regional control among ER- tumors (HR=0.87 (0.28-2.67)). Similar results were found in the low-risk HYPO cohort (Figure 2) with significantly worse OS in the ER- /”low TILs” tumors as compared to ER- /”high TILs” tumors (HR=0.30 (0.09 -1.05)), with no effect of TILs found for patients with ER+ disease (interaction test p=0.045). Same trend was seen for DM, but significance was not obtained, probably due to very low event rates.