The prognostic and predictive role of the neutrophil-to-lymphocyte ratio and the monocyte-to-lymphocyte ratio in early breast cancer, especially in the HER2+ subtype

Systemic inflammatory state of the host and the inflammatory response in the tumor microenvironment have a remarkable impact on cancer progression [1, 2]. Neutrophils secrete cytokines that promote cancer growth [3], and they may also suppress the immune responses mediated by lymphocytes [4]. Furthermore, monocytes are able to suppress lymphocyte activation and enhance tumor progression [5]. On the other hand, lymphocytes have an important role in the immune responses against cancer both in the circulation and in the tumor microenvironment, e.g., via T-cell mediated cellular cytotoxicity [6]. Therefore, the blood neutrophil-to-lymphocyte ratio (NLR) and monocyte-to-lymphocyte ratio (MLR) can be considered as indicators of the host’s systemic inflammatory state [7], i.e., high NLR and MLR may reflect poor anti-tumor immunity.

Several studies have investigated the prognostic role of NLR in breast cancer (BC) [7]. In two rather recent meta-analyses, a high NLR was shown to predict poor overall survival (OS) and disease free survival (DFS) among BC patients [8, 9]. The associations were evident especially among those patients with hormone receptor (HR) negative and/or human epidermal growth factor receptor 2 (HER2) negative BC but less clear among the HER2+ patients [8, 9]. The impact of MLR on BC prognosis has been less extensively studied. Some publications suggest that a high MLR associates with a poor outcome in BC [7, 10] but there are also studies reporting no correlation between MLR and BC outcome [7, 11].

One of the major advances in the treatment of BC has been the development of trastuzumab, a HER2 antibody, which has remarkably improved the outcome of HER2+ patients [12]. A part of trastuzumab’s anti-tumor effects are mediated via the immune system, especially through antibody-dependent cellular cytotoxicity (ADCC) [6]. First, trastuzumab binds to the surface of cancer cells and activates the innate immune response, resulting in the death of cancer cells by macrophages and natural killer (NK) cells. Dying cancer cells release trastuzumab-coated antigens, which activate cytotoxic T-lymphocytes leading to an adaptive immune response and death of the cancer cells presenting this antigen [6]. Indeed, high levels of tumor infiltrating lymphocytes (TILs) have been shown to associate with a better response to trastuzumab in HER2+ BC [13]. There are only a few studies investigating the possible predictive role of the blood inflammatory cells in HER2+ BC treated with trastuzumab, and the results have been conflicting [14‐16].

The aim of this study was to investigate the prognostic impact of both NLR and MLR in a material of 209 BC patients, 107 of them HER2+. Patients were diagnosed between 2001 and 2008 and 40% of the HER2+ patients had received adjuvant trastuzumab, since adjuvant trastuzumab only became widely available in Finland in 2005. Thus, this material provides a rather unique opportunity to investigate also if these two markers of systemic inflammation, NLR and MLR, have a predictive role regarding the efficacy of adjuvant trastuzumab treatment.

The WBC differential was available for 209 eligible patients (107 HER2+ and 102 HER2−) and the demographics of these cases are presented in Table 1. The median follow-up time was 10.4 years (range 0.5–15.2). Median age was 58.1 years (range 32.3–82.7) and 35% of the patients were premenopausal (Table 1). Deaths and breast cancer relapses occurred more often among the HER2+ patients than among the HER2− patients (p ≤ 0.006) (Table 1).

Median time from the BC surgery to the blood sample collection was 6.0 weeks (range 0.3–12.8). The optimal cut-off-points calculated with the ROC curve were 2.2 for NLR (AUC 0.624, 95% CI 0.54–0.71, p = 0.006) and 0.22 for MLR (AUC 0.597, 95% CI 0.51–0.68, p = 0.031). High NLR (≥ 2.2) was found in 35% and high MLR (≥ 0.22) in 43% of the patients (Table 1). In the HER2+ subgroup, a high NLR was found in 38% and a high MLR in 42% of the patients; the corresponding values in the HER2− subgroup were 31% for high NLR and 43% for high MLR (Table 1). Similarly, in the HR+ subgroup (n = 150), a high NLR was found in 35% and a high MLR in 41% of the patients, and the corresponding values in the HR− subgroup (n = 59) were 34% for high NLR and 46% for high MLR. There were no correlations between NLR or MLR and standard prognostic factors, i.e., tumor size, nodal status, grade, HER2 or HR status (data not shown).

In this study, we found that the outcome of the HER2+ BC patients with a high NLR or MLR was poor if their adjuvant treatment did not include trastuzumab. Trastuzumab was especially beneficial for those HER2+ patients with a high baseline NLR or MLR, while the survival of the HER2+ patients with a low NLR or MLR was good irrespective if they received adjuvant trastuzumab. Both high NLR and MLR correlated with poor survival also in the whole patient material and in HR+ and HR− subgroups.

Based on the results emerging from the present study, we hypothesize that trastuzumab modulates the systemic inflammatory state of the host and overcomes the poor prognostic impact of high baseline NLR and MLR. Indeed, it has been shown in advanced HER2+ BC that after one cycle of trastuzumab emtansine the blood lymphocyte counts were elevated, resulting in a decreased NLR and improved outcome [19]. In another study, after one cycle of trastuzumab, the neutrophil count decreased among patients exhibiting a response to trastuzumab but increased among those who did not benefit from trastuzumab [20]. It is also known that at least some chemotherapeutic agents have immune-modulatory effects, e.g., paclitaxel may sensitize tumor cells to cytotoxic T-lymphocyte mediated cell death [21] which also plays a crucial role in trastuzumab’s mechanism of action. Thus, the synergistic effect of trastuzumab with chemotherapy, especially with taxanes, seems to be at least in part explained by the improvement in the anti-tumor immune response [22]. Since in the present study the patients received trastuzumab in combination with chemotherapy, 81% with taxane, it is not possible to analyse if the possible immune-modulatory effect is due to trastuzumab alone, chemotherapy or both.

The host’s inflammatory state also seems to influence on the efficacy of immuno-oncological (IO) treatments, e.g., programmed death-1/programmed death ligand-1 (PD-1/PD-L1) inhibitors. In recent years, IO-treatments have shown remarkable efficacy in many cancer types but in BC only a small subset of patients obtain long-lasting responses [23]. It is important to understand the mechanisms behind treatment responses to expand the proportion of patients benefiting from these treatments. A high NLR has been reported to be a marker of poor prognosis also in cancer patients treated with PD-1/PD-L1 inhibitors [24]. Thus, trastuzumab’s possible ability to modulate the blood lymphocyte and neutrophil counts provides a rationale for combining trastuzumab with IO-treatments. In fact, there are ongoing clinical trials investigating the efficacy of these combination treatment strategies [23]. Furthermore, it would be important to understand the mechanisms behind the increased NLR/MLR as they may reveal new risk factors for poor outcome in BC. In many diseases, such as cancer, infections or chronic inflammatory diseases, a high NLR/MLR might reflect the state of host’s systemic inflammation before the illness, the immunological response mounted against the illness or some aspects of the illness itself. Interestingly, the new COVID-19-infection seems to be especially serious among patients with a high NLR [25] and more often severe also among patients with chronic inflammatory conditions. Here, NLR or MLR did not correlate with the standard prognostic factors, suggesting that in BC NLR and MLR are not a consequence of the aggressiveness or extent of the cancer itself but otherwise modulate tumor progression and treatment responses.

One recent retrospective study has compared the prognostic value of the NLR among HER2+ patients treated with or without adjuvant trastuzumab [16]. In contrast to our results, NLR was not prognostic among HER2+ patients treated without trastuzumab but showed prognostic value among the patients with 1-year adjuvant trastuzumab. The difference in the 3-year DFS rate was rather small, 95.3% vs. 90.5% for low and high NLR groups, respectively, with a rather short median follow-up time of 20 months [16]. In our study, with a long follow-up time (median 10.4 years), the prognostic impact of both NLR and MLR according to OS, BCSS and distant relapse rate was found among the HER2+ patients treated without adjuvant trastuzumab but not among those who did receive trastuzumab. Importantly, NLR remained as a significant prognostic factor for OS also in the COX multivariate analysis. There are several explanations for these contradicting results, e.g., there are differences in determining the optimal cut-off-point for NLR, in the timing of the pre-treatment blood samples, in the treatments received in addition to trastuzumab and in the length of trastuzumab treatment. Furthermore, there is no knowledge of the inflammatory state of the tumor microenvironment, e.g., TILs, tumor associated macrophages (TAMs) and NK-cells, all of which probably exert an influence on the response to trastuzumab [6].

In line with previous studies [9], a high NLR correlated here with poor survival among the HR− patients, but also in the HR+ subgroup. A long follow-up period for survival and BC specific outcomes may be especially important in HR+ BC in which the recurrences often occur quite late. Furthermore, we found a correlation between MLR and survival among the HER2+, HR+ and HR− patients suggesting that also monocytes have an important role in BC progression. Instead, in the HER2− and triple-negative subgroups, we did not find statistically significant correlations between NLR or MLR and survival, but among the HER2− patients the number of events was rather small, and the triple-negative subgroup was too small for reliable statistical analyses.

The strengths of our study include its unique patient material in which approximately half of the HER2+ patients had received adjuvant trastuzumab. Two other strengths are the long follow-up period and reliable patient records. This study has also limitations; first, since this is a retrospective observational study, the causal relationships between the investigated factors remain hypothetical. Second, chemotherapy was administered more often to patients who received adjuvant trastuzumab compared to those who did not, which must be considered in the interpretation of the results since also chemotherapy may modulate inflammatory responses as discussed above. Third, the number of patients in some of the subgroup analyses was small. Thus, the results will need to be confirmed in larger randomized studies.