The NLR has been proposed as a prognostic marker in early breast cancer, with higher values indicating a pro-inflammatory and immune-suppressed state [4] associated with a poorer prognosis in terms of relapse and survival [12]. However, the uncertainties surrounding its biological significance and the omission of baseline NLR as a covariate in the validated prognostic models of early breast cancer [13] prompted this study of a cohort of early BC patients treated with contemporary adjuvant and neoadjuvant standards. Beyond the absence of prognostic impact of NLR in early BC patients, the primary finding of this study is the lack of correlation between NLR and tumor lymphocytic infiltration and between NLR and other tumor characteristics.

NLR was only elevated in premenopausal patients, an unexpected finding since higher NLR levels have been reported in older women [30]. We did not identify any association of NLR with higher tumor stage or more aggressive biological traits, except for a weak association with tumor proliferation as assessed through Ki67 immunohistochemistry, the implications of which also remain uncertain. The assessment of the correlation between NLR and sTIL represented the main objective of this study, considering the relevance of understanding the biological correlation of peripheral and tissue immune-related prognostic factors to improve its clinical applicability. In this work, no association between both immune markers was found. The correlation between NLR and sTIL has been previously evaluated, also without finding any link between them. However, the evidence has been limited until now, with studies characterized by small sample size and predominantly focused on TNBC [22, 23, 31,32,33]. Thus, our work confirms the absence of a relationship between two widely used immune biomarkers, NLR and sTIL, across all subtypes of early BC. These results remained unchanged when variables were analyzed categorically and in analyses stratified by subtypes and levels of lymphocytic infiltration. These findings strongly suggest the lack of association between NLR levels and the degree of immune response activation in the tumor.

The cutoff for NLR is a relevant issue for the interpretation of our data. In this study we decided to analyse NLR as a continuous variable to avoid the loss of information caused by dichotomization and the usual overfitting for models developed using ROC curves to determine the cutoff. However, the analysis with both the median value and 3 as cut points did not show any difference in the risk of death or recurrence. These cutoffs are in fact below the usual cutoff of 4 used in other tumors with higher inflammatory activation, such as pancreatic or renal cancer [19, 20]. It is noteworthy that the median NLR in our cohort was 1.96, close to the median range of 1.60–1.80 which is generally considered as normal in population-based studies [18]. While inflammatory activation contributes to BC progression [34], the observed NLR levels might suggest a comparatively less inflammatory systemic tumor environment in early BC patients. This also suggest a lesser degree of impairment in the anti-tumor immune response compared with other neoplasms or with advanced disease. In this context, we could expect a lower impact of NLR in the prognosis of early BC, except in cases with extreme values.

The patient population included in this study displays the expected distribution of tumor subtypes in early BC. Our data indicate no difference of NLR levels among BC subtypes, nor do they show any different prognostic impact within any of them, including TNBC, for which prior reports have suggested a greater relevance of NLR. These results disagree with those reported by Jia et al. in a Chinese cohort of 1570 patients, mostly treated with adjuvant chemotherapy, and in which a NLR cutoff of 2 was used [35]. However, the referenced study entirely excluded patients treated with neoadjuvant chemotherapy, who represents approximately half of our cohort. Several other studies with sample sizes exceeding 500 patients have similarly shown a prognostic value of NLR in early BC. It is noteworthy, however, that these studies solely considered patients treated in the adjuvant setting. Additionally, certain confusion factors, such as the inclusion of in situ carcinomas [36] or the administration of NSAIDs [37], were present. Another study conducted by Koh et al., the largest reported thus far, also found a relevant prognostic impact for NLR in TNBC [38]. Remarkably, this is the only study that, similarly to ours, includes patients treated in the neoadjuvant setting (although only 15%) and incorporates treatment-related variables in the multivariate model. However, between 16% and 32% of patients within 4th and 5th quintiles of NLR (quintiles showing a difference in terms of DFS and OS) had metastatic disease at time of inclusion. The divergence in NLR’s prognostic impact between these studies and our findings might also be attributed to differences in inclusion periods (all of them before 2011), which correspond to different therapeutic standards, as well as to the lack of inclusion in all of them of some prognostic factors such as Ki67 and grade. Finally, the geographical origin of the patients may have also played a relevant role, considering that a recent meta-analysis, focused on the neoadjuvant setting, showed significant disparities in the prognostic impact of NLR according to geographic location. Interestingly, no effect of NLR on DFS was found in non-Asian populations [39]. In any event, our results do not replicate the previous reported differences in the risk of recurrence or death and suggest the absence of prognostic value for NLR in the context of early BC treated with contemporary adjuvant or neoadjuvant standards when accounting for other prognostic variables in the multivariate models.

Our work has several limitations. First, we examined a high-risk BC cohort, predominantly composed of patients treated with adjuvant or neoadjuvant chemotherapy, although this is precisely the clinical context in which new biomarkers are more necessary to allow new escalation or de-escalation therapeutic strategies. Second, the sample size and number of events gave us adequate statistical power to exclude moderate prognostic effects (HR around 2), but we cannot discard milder effects of NLR on the risk of BC recurrence or death. However, the HR reported in NLR studies for early BC fall within the range of 1.50–2.50 in the publication by Koh et al. [38] and tend to be equal or over 2 in most studies [35, 37] and in the main meta-analysis [12]. Third, although sTIL were evaluated according to international standards, the evaluation was performed by a single pathologist. Fourth, sTIL is an imperfect biomarker of immune response in the tumor microenvironment. Although our data demonstrate no association with the NLR levels, the assessment of other immune biomarkers either in the primary tumor or in plasma samples, might allow a better understanding of the role of NLR, if any, in the immune response status of early BC patients.

In conclusion, the results of our study did not establish any correlation between NLR and tumor-infiltrating lymphocytes –a biomarker of tumor immune response—nor with other biological factors relevant for tumor progression. Furthermore, we were unable to replicate, within a contemporary Western cohort of early BC patients, prior findings that supported a prognostic impact of NLR, either in the whole group or in any BC subtype. Taken together, our findings suggest that NLR is neither a substantial prognostic factor nor a valid biomarker for tumor immune response, thus questioning its clinical utility in the context of early BC. Perhaps it is time to consider not including NLR in early breast cancer prognostic studies, especially in non-Asian populations.