Significance of baseline neutrophil-to-lymphocyte ratio for progression-free survival of patients with HER2-positive breast cancer treated with trastuzumab emtansine

The efficacy of trastuzumab emtansine (T-DM1) is prolonged for some patients; however, the predictive factors remain unknown. We focused on a peripheral blood biomarker, the neutrophil-to-lymphocyte ratio (NLR), regarding T-DM1 treatment efficacy. Fifty-three advanced or metastatic breast cancers treated with T-DM1 were retrospectively recruited from three institutes. The NLR in the peripheral blood was measured at baseline and after one cycle. The cutoff value of the NLR was set at median value 2.56. The progression-free survival (PFS) of patients with NLR-low at baseline (n = 26; median, not reached) was significantly better than that of patients with NLR-high (n = 27; median, 4.13 months; hazard ratio [HR], 0.226; 95% confidence interval [CI], 0.112–0.493; p = 0.0001). Longer overall survival was significantly associated with a low NLR (HR, 0.384; 95% CI, 0.170–0.910; p = 0.0296). In the subgroup analysis, patients with NLR-low consistently had longer PFS compared to those with NLR-high irrespective of the number of prior chemotherapy regimens, prior trastuzumab, visceral metastasis, estrogen receptor status, and human epidermal growth factor receptor 2 (HER2) score. Although detailed mechanisms remain unknown, treatment efficacy of T-DM1 may be partly mediated by activation of the immune system. Low baseline NLR appears to be beneficial for treatment with T-DM1 in HER2-positive breast cancers.