Immunological predictors of the therapeutic efficacy of atezolizumab in combination with nab-paclitaxel in metastatic triple-negative breast cancer: A pilot multicenter retrospective associative study

Background. Chemoimmunotherapy with the combination of atezolizumab and nab-paclitaxel demonstrates clinical benefit at 12 months in only 45.8% of patients with metastatic triple-negative PD-L1-expressing breast cancer. This emphasizes the relevance of finding predictor markers of high sensitivity to immunotherapy. Since atezolizumab acts through the local immune system, assessing its status prior to therapy administration may be crucial. Aim. The objective of this study was to evaluate the predictor significance of immunological parameters of tumour microenvironment in patients with metastatic triple-negative cancer receiving therapy with atezolizumab in combination with nab-paclitaxel. Materials and methods. Eleven patients with metastatic triple-negative breast cancer, who received atezolizumab in combination with nab-paclitaxel, were included in the study. Among them, five patients exhibited a durable response (progression-free survival 6 months), while six patients had a short response (progression-free survival ≤6 months). Tumour microenvironment parameters (the proportion of immune cells in the microenvironment and their expression of PD-L1 and PD-1) were analyzed by TSA-associated multiplex immunofluorescence (Tyramide Signal Amplification) using the Vectra® 3.0 tissue analysis system and InForm® software (Akoya Bio, USA). Results. The study revealed that CD163+-macrophage counts below 6.475% of all tumor stromal cells were associated with long-term efficacy of atezolizumab in combination with nab-paclitaxel in patients with metastatic triple-negative cancer. Conclusion. The number of CD163+-macrophages in the tumor stroma could potentially serve as a marker for predicting the efficacy of atezolizumab in combination with nab-paclitaxel in patients with metastatic triple-negative cancer.