Blood routine test results, which reflect the individual’s system or local status, also have certain application value for cancer diagnosis (26). For example, neutrophils can produce cytokines, chemokines, and growth factors that promote angiogenesis, tumor cell proliferation and migration in the tumor microenvironment (27). Platelets, an important part of the blood clotting system, also can contribute to cancer-favored inflammation response (28), and high platelet counts were reported to be associated with adverse outcomes in BC (29). In contrast, lymphocytes in the blood are thought to can reflect the status of anti-tumor immunity (30). Based on the precious findings, NLR, MLR and PLR, which reflect the balance between inflammatory and immune response in cancer, have attracted more and more attention from researchers (31). However, with the increase of the number of studies, the value of these BIMs in BC especially in predicting the response to NACT, has become controversial. Furthermore, few studies have simultaneously compared the value of these BIMs in predicting response to NACT.
In this study, we found that there was no difference in the BIMs before chemotherapy between the pCR group and the non-pCR group. However, the NLR, MLR and PLR in the pCR group all were significantly lower than those in the non-pCR group after NACT. This suggested that pCR might be easier to achieve in patients with weaker systemic inflammatory response after chemotherapy. ROC analysis showed that PLR, with 65% sensitivity and 73% specificity, had the largest AUC compared to NLR and MLR. Univariate analysis showed that parameters such as ER, PR, HER2, NLR, MLR, PLR were significantly associated with pCR. But multivariate logistic regression analysis showed that only HER2 and PLR were independently predictive factors of pCR.
It is well known that HER2 was a positive predictor for BC patients with the application of anti-HER2 targeted drugs (32). Especially for patients receiving trastuzumab plus pertuzumab during NACT, the pCR rate even can reach more than 60% (33). Our results also support this conclusion. Although NLR and MLR after chemotherapy were associated with pCR rates in univariate analysis, they did not show statistical significance in multivariate analysis and survival analysis. The insignificance of their results might be attributed to the fact that the neutrophil and monocyte counts could be disturbed because of most patients were injected with granulocyte stimulating factor to prevent the neutropenia after chemotherapy. The incidence of thrombocytopenia during NACT was relatively low in this study, and patients were less likely to be treated for thrombocytopenia. Therefore, the platelet count could reflect the patient's actual condition.
In addition to the role in hemostasis, platelets have been also thought to play an important role in promoting tumor progression and metastasis. First, platelets can produce a variety of cytokines such as platelet-derived growth factors and vascular endothelial growth factor A, to stimulate tumor progression and dissemination. Second, platelets can induce the epithelial–mesenchymal switch of tumor cells, reduce tumor cell anoikis in the blood. Third, platelets can protect tumor cells from being recognized by immune cells through forming a cell–fibrin–platelet aggregate surrounding tumor cells in the circulation. This is thought to play an important role in contributing to tumor metastasis (10, 34). Therefore, the dynamics of PLR represents the disorder of inflammatory - immune status of patients. Prior to the present study, there have been some studies that used PLR as a predictive marker for NACT in BC. Some reported that increased PLR during chemotherapy predicted higher pCR rate, while others had the opposite conclusions (35, 36). A meta-analysis has demonstrated that increased PLR during NACT could be as a prognostic biomarker for poor overall survival and DFS (37). Our results supported that increased PLR suggested poor efficacy of NACT.
Some researchers believed that cell component in blood might can provide information about the status of tumor microenvironment, since most inflammation and immune cells in tumor microenvironment were derived from peripheral blood (16). However, there are few studies to investigate the relationship between peripheral blood cells and corresponding infiltrating cells in tumor stroma. One important reason is the lack of a specific marker to label the same type of cells in both blood and stroma. P-selectin, also known as CD62P, is stored in α-granules and Weibel–Palade bodies of platelets and endothelial cells, respectively. P-selectin expression is considered to be a marker of platelet activation. P-selectin on activated platelets can mediate interactions with monocytes, instigating paracrine-signaling mechanisms that lead to enhanced inflammation, as well as inducing factors that trigger thrombosis (38). In this study, P-selectin staining was performed on the specimens of 125 patients. The results showed that the expression of P-selectin in tumor microenvironment was significantly positively correlated with PLR, suggesting that the expression of P-selectin in stroma might be affected by platelets in peripheral blood, but the mechanism needs to be further studied.
There are still some limitations in this study. First, this is a single-center retrospective study with a small sample size and the follow-up time is short, which makes some conclusions less convincing. Second, although P-selectin is thought to be expressed mainly on activated platelets, it is not a platelet-specific marker. The expression levels of P-selectin in tissues were not exactly equivalent to TEPs. Therefore, the significance of correlation analysis between P-selectin and PLR remains to be further explored.