Though our results indicate that elevated PLR was significantly predictive of worse PFS in patients treated with 1st or 2nd generation EGFR TKIs, comparable to the study conducted by Liu et al.[28], the relationship was not apparent in patients managed with 3rd gen EGFR TKIs. Our study suggests that osimertinib may be equally efficacious in patients regardless of negative prognostic markers. Though clinical data supports the superior survival outcomes of osimertinib compared to 1st /2nd generation TKIs [26], an explanation for the discrepancy in laboratory markers is not currently identified in the literature.
Prior studies have identified changes in the tumor microenvironment in response to management with EGFR TKIs, resulting in changes including alterations in the populations of tumor infiltrating lymphocytes (TILs), such as an increase number of effector CD8 + T cells and increased antitumor CD4 + T cells, increased M1 tumor-associated macrophages (TAMs) and decreased M2 TAMs, increased MHC I and MHC II expression, and increased secretion of pro-inflammatory cytokines [29, 30]. Additionally, it has been previously found that improvements in survival outcomes in multiple cancer types correlate with changes in peripheral cell counts, specifically an overall decrease in platelet count and an increase in ALC [5, 9, 10, 12, 31–33]. However, differences in tumor microenvironment changes dependent on the generation of EGFR TKI are not currently defined in the literature.
Our findings revealing changes in laboratory values at different time points in patients treated with 3rd gen TKIs compared to patients treated with 1st /2nd gen TKIs may suggest differences in tumor microenvironment response and the systemic pro-inflammatory state depending on the generation of TKI received. Though these reported changes were not statistically significant, they reveal an interesting trend. While the decrease in ANC and platelet count in patients managed with osimertinib are consistent with the laboratory changes associated with improved survival outcomes, the decrease in ALC, most notably at 6 weeks after treatment initiation, is surprising since prior studies have identified an increase in ALC correlating with improved survival and that a decrease in ALC over time could be suggestive of decreased T cell infiltration and activation as seen in osimertinib resistance [34]. This suggests that the efficacy of EGFR TKIs may be dependent on a functional immune system. However, because lymphocytes are inherently heterogenous, the reliability of using ALC as a biomarker for improved survival may have limited utility.
Further stratification of PLR by additional clinical variables, particularly BMI, trended towards worse median progression free survival identifiable in the 1st /2nd gen group. Though results were not statistically significant, we believe combining multiple clinical prognostic markers may warrant further investigation using larger sample sizes.
Notably, our multivariate analysis failed to identify a single laboratory biomarker associated with worse PFS in either treatment group while holding all other variables constant. This suggests that the reliance on a single laboratory datapoint to accurately prognosticate patients treated with EGFR TKIs may be limited, particularly in patients managed with osimertinib. We therefore suggest PLR be used in combination with other variables, such as performance status, to accurately predict pre-treatment survival outcomes.
Our study has notable limitations, particularly due to its retrospective study design. Additionally, our conclusions resulting from stratifying PLR by albumin and BMI are limited by low sample size. Last, patients who were treated with osimertinib were generally treated in more recent years compared to patients treated with 1st /2nd gen EGFR TKIs due to its FDA approval in 2018 for use in EGFR mutated patients in the first-line setting.
Further studies evaluating the tumor microenvironment differences in patients receiving 3rd generation EGFR TKIs versus 1st /2nd generation EGFR TKIs are warranted to help illustrate how 3rd gen TKIs may be more efficacious. Additionally, more studies may help determine if PLR should be considered as a reliable outcome predictor in EGFR mutant NSCLC patients receiving TKIs and to better understand trends in peripheral cell counts in patients treated with 3rd generation EGFR TKIs.