Predictive and prognostic role of peripheral blood eosinophil count in triple negative and hormone receptor negative/HER2 positive breast cancers patients undergoing neoadjuvant treatment.

Introduction: In clinical practices, up to 27% of breast cancer (BC) patients receive neoadjuvant chemotherapy (NAC). In this context, a pathological complete response (pCR) is the most commonly used end-point. High pCR rate is frequently associated with tumor infiltrating lymphocytes. Besides, circulating immune cells are also often linked to chemotherapy response.
Materials and methods: We performed a retrospective analysis on 112 BC patients (79 triple negative, 33 HR-/HER2+), treated with standard NAC. The median follow-up was 37.5 months (range 9-156). Eosinophil and lymphocyte count were collected at baseline, after surgery, at 1 year of follow-up and at relapse. The primary end-point is the association between the relative eosinophil count (REC) and pCR. The secondary end-points are the associations of REC, relative lymphocyte count (RLC) and eosinophil/lymphocyte product (ELP) with relapse, disease free (DFS) and breast cancer specific (BCSS) survival and to study the variation of REC and RLC during follow-up.
Results: We observed a higher pCR rate in patients with REC≥1.5% vs patients with REC <1.5% (55.6% vs 36.2%, p = 0.04), and a higher median REC in patients with pCR (1.9% vs 1.2%, p 0.042). No statistically significant associations were detected with relapse, nor between RLC with pCR or relapse. We observed a 3-year BCSS of 91% vs 80% for high and low REC respectively (p 0.05; HR 0.336, 95% CI 0.107-1.058) and of 88% vs 49% in RLC≥17.5% and <17.5% respectively (p 0.01; HR 0.217, 95% CI 0.060-0.783). No significant differences were detected for DFS. Combining the two parameters in the ELP, we observed an association with pCR (59.6% in ELP≥35.8 vs 30.9% in ELP<35.8, p 0.002), relapse (12.3% vs 29.1% in high and low ELP, p 0.028), DFS (3-year DFS 90% vs 69% in high and low ELP, p 0.012; HR 0.337, 95% CI 0.138-0.823) and BCSS (3-year BCSS 95% vs 75% in high and low ELP, p 0.001; HR 0.129, 95% CI 0.029-0.573). Moreover, we observed a raise of REC after surgery from 1.4% to 2.6% (p 0.0001) and a significant reduction at relapse from 2.8% to 1.7% (p 0.021). Conversely, a reduction of RLC from 26.9% at baseline to 20.45% after surgery (p 0.0001), without significant variation at relapse, was detected.
Conclusion: REC, RLC and ELP could be new promising, affordable and accessible biomarkers predictive for NAC response and prognostic for longer survival in TNBC and HR-/HER2+ BC. Confirmation in a larger cohort is needed.