Modulation by treatment of tumor infiltrating lymphocytes (TILs) and PDL1 expression in triple-negative breast cancer in the ETNA trial.

Abstract

555 Background: We assessed TILs and PDL1 expression before, during and after neoadjuvant treatment in TNBC patients enrolled in the ETNA study, and investigated associations with clinical outcome. Methods: In ETNA patients randomly received paclitaxel or nab-paclitaxel followed by 4 cycles of an anthracycline regimen, including 219 centrally confirmed TNBC. We successfully measured stromal and intratumoral TILs (sTILs, iTILs) and PDL1 status (Ventana SP142, IC≥1%) on biopsies before [n = 186/213 (84.9%)], on d1 cycle 2 (d1c2) of therapy [n = 41/186 (22.0%)], and at surgery [SX, n = 65/129 (34.9%)]. We investigated the expression and modulation over time of TILs and PDL1 and their association with pCR and event-free survival (EFS). Results: Prevalence of PDL1+ was 35.5% (baseline), 20.6% (d1c2) and 30.1% (SX). At each time-point sTILs and iTILs were higher in PDL1+ cases (p≤0.01). An effect of age of the tumor blocks (5-7.5 years) or pre-analytical issues could not be ruled out for the relatively low rate of PDL1 positivity. Paired PDL1 at baseline and d1c2 showed conversion in 25.7% (pos to neg [11.4%] or neg to pos [14.3%]). Comparing PDL1 at baseline and SX, the conversion rate was 30% (pos to neg [8.3%] or neg to pos [21.6%]). sTILs and iTILs significantly increased at cycle 2, more significantly in pCR (p≤0.001) than in RD (p≤0.05) cases, and a not significant trend of decrease was observed at surgery PDL1+ tumors had a higher pCR rate (54.7% vs 32.5%, p = 0.004). PDL1 retained significance (OR 2.00 [1.04-3.88], p = 0.039) after adjustment for sTILs (OR 1.21 [1.03-1.42], p = 0.021). High iTILs and sTILs at d1c2, but not PDL1 status, were predictive of pCR. Notably, adjusting for sTILs, PDL1+ tumors at d1c2 showed a trend for association with lower pCR rate (OR 0.06 [0.01-1.15], p = 0.062). sTILs at cycle 2 was the most informative variable (OR 1.61 [1.28-1.61], p = 0.004) and provided independent information to baseline biomarkers. Baseline PDL1 and biomarkers at cycle 2 were not associated with EFS. In surgical samples with RD, higher sTILs, but not iTILs and PDL1 status, were associated with a trend for a lower risk of recurrence (HR 0.19 [0.02-1.39], p = 0.068). Conclusions: sTILs assessment on core biopsies after one cycle of taxane is a promising early biomarker of pCR. PDL1, as well as sTILs and iTILs, provided independent prediction of pCR and were strongly modulated by treatment. The modulation of PDL1 expression should be considered whenever PDL1 is assessed in view of identifying candidates to atezolizumab in 1st line advanced setting.