The ratio of PD1+CD8+T cells in stromal area of tumor tissue is associated with the effect of neoadjuvant chemotherapy in HER2 negative breast cancer patients.

e12626 Background: For patients diagnosed with early breast cancer, surgery remains the standard of care. Early patients achieving pathological complete response (pCR) after neoadjuvant therapy have been proved to be associated with improved survival. However, the accurate prediction of pCR in a clinical setting remains challenging. Tumor infiltrating lymphocyte (TIL) levels have recently been identified as an independent predictor of pCR in breast cancer. However, due to extremely complex tumor microenvironment within tumor, the role of different immune cell subtypes in neoadjuvant chemotherapy (NAC) is inconclusive. This study aimed to explore the potentially predictive role and dynamic changes of immune cell subsets in patients with HER2 negative breast cancer receiving NAC. Methods: Since January 2020, tumor tissue samples of 12 HER2 negative breast cancer patients were collected at baseline and after NAC. Several kinds of immune cells including CD3+T cells, CD4+T cells, CD8+T cells, PD-1+CD8+T cells, Tregs, M1/M2 tumor associated macrophages(TAM), PD-L1+CD68+TAM, B cells, CD56bright NK cells and CD56dim NK cells in the tumor tissue were evaluated by multiple fluorescence immunohistochemistry (mIHC) and counted in intratumoral and stromal area for density and ratio. T test was used for the comparison of immune cells and statistical significance was set at p = 0.05. Results: We examined immune cell subtypes and PD-L1/PD-1 expression of 12 HER2 negative breast cancer patients. According to achieving pCR or not, these 12 patients were divided into two groups, pCR (n = 3) and non-pCR group (n = 9). The results showed that the ratio of PD1+CD8+T cells in stromal area of baseline tumor tissue of pCR group was significantly higher than non-pCR group (median ratio, pCR group vs. non-pCR group = 17.3% vs. 3.6%, p = 0.029).In addition, the ratio of PD1+CD8+T cells in stromal area of pCR group was still significantly higher than that of non pCR patients after NAC (median ratio, pCR group vs. non-pCR group = 20.7% vs. 2.6%, p = 0.0003). Conclusions: Whether at baseline or after NAC, the ratio of PD1+CD8+T cells in stromal area is associated with the effect of NAC in HER2 negative breast cancer.