The investigations and research on prognostic markers are very crucial particularly among cancer patients as they aid in the improvement of existing and development of newer treatment therapies and patient care. Previous meta-analyses have only analyzed survival outcomes with different types of cancers including lung cancer. To our knowledge, this is the first meta-analysis to assess the prognostic significance of MPV with survival outcome among lung cancer patients only.
A meta-analysis by Pyo et al. in 2016 showed that MPV levels in patients with malignant tumors were significantly higher than in healthy subjects. However, in lung cancer, the MPV of pre-treatment patients was lower than that of healthy subjects but not statistically significant (mean difference − 0.352, 95% CI − 0.763 to 0.060).13 A recent meta-analysis found no significant association between MPV levels and survival outcomes among cancer patients. While doing subgroup analysis including 7 studies, higher MPV levels were not associated with worse OS (NSCLC: HR 0.85, 95% CI 0.64 to 1.15).14 Our study included 11 studies with NSCLC, SCLC, and NSCLC + SCLC, and similar to the above studies showed no statistically significant association.
Subgroup analysis was conducted by country of origin, cut-off value, tumor stage and tumor type, type of analysis. All the subgroups showed insignificant association with MPV values and OS. While in DFS, a significant association was shown between low MPV and worse DFS in a univariate analysis. But we believe this result requires verifying the prognostic significance of a univariate in the validation cohort since the univariate analysis actually has a high risk of bias leading to overestimation of sensitivity and specificity in predicting cancer prognosis. Interestingly, worse DFS was shown to be significantly associated with MPV values among advanced cancer patients. These findings are similar to a study showing MPV levels in patients in an early-stage lung cancer similar to those found in healthy subjects and increased with the cancer progression.31 However, the result cannot be generalized considering few studies and sample size.
Platelet volume is determined during both megakaryopoiesis and thrombopoiesis. Various stages of platelet production and maturation are influenced by cytokines like interleukin-6 (IL-6), granulocyte colony-stimulating factor (G-CSF), and macrophage colony-stimulating factor (M-CSF).32 Moreover, platelets can get activated on encountering circulating tumor cells which result in the formation of microparticles that can potentially promote the invasiveness of tumor cells.33 Therefore, this close interplay between high MPV and poor prognosis of cancers can be a reasonable hypothesis. In contrast, our findings do not support the hypothesis that an MPV level is a prognostic factor for poor outcomes in lung cancer patients.
The strength of our study lies in the fact that this is the first meta-analysis to show the association between MPV levels and survival outcomes in lung cancer patients. In contrast to previously published meta-analyses, our study results enable a deeper comprehensive understanding of the predictive role of MPV in lung cancer. However, there are still several limitations in our work. The inclusion of retrospective studies and inclusion of studies published in the English language only might have added biases of any form in our study and excluded probable other studies. Second, studies provided HRs and 95% CIs from univariable analyses, which could lead to bias towards the overestimation of the prognostic role of the MPV, as the HR in multivariable analyses may not be statistically significant after the consideration of other elements. In addition, as with all meta-analyses, heterogeneity resulting from various factors as depicted in the subgroup analysis may have the potential to affect the interpretation of the results. Lastly, the clinical application of MPV in predicting DFS mandates further verification due to the lack of a standardized cut-off value.