In this study, we explored whether patient age and their ECOG PS had a potentially positive effect on the efficacy of ICIs. To clarify the predictive value of age and ECOG PS in lung carcinoma when using ICIs, we performed this meta-analysis and pooled the HRs for the OS and PFS rates. Our results showed that ICIs increased the OS and PFS rates in both age groups when the cut-off value was set at 65 years and in the ECOG PS 0 and 1 groups among patients diagnosed with advanced lung cancer. The remaining results demonstrated that when patients were divided into three groups (< 65, 65–74, and ≥ 75 years), no benefit was noted for those aged 65–74 and ≥ 75 years.
These results showed that younger and older patients could benefit from ICIs with respect to OS and PFS rates when the cut-off of 65 years is used. There was a trend toward better long-term survival outcomes in younger patients, although the difference between the two groups was not significant. Similarly, one study found an OS benefit in patients treated with immunotherapy in different age groups [8]. A study reported that the OS and PFS rates were better in younger and older patients when using ICIs than in controls, but older patients could gain more benefits from ICIs than younger patients [6]. When the patients were divided into three groups by age, our results showed that only those aged < 65 years could benefit from ICIs, and those aged 65–74 and ≥ 75 years were unlikely to benefit in terms of OS. Likewise, another meta-analysis showed that no OS benefit was observed in patients aged ≥ 65 years treated with PD-1 inhibitors [42]. However, Corbaux et al. [43] reported that patients treated with single-agent ICIs for various cancer types had greater OS and PFS rates, especially when they were older than 70 years. There may be several reasons for these inconsistent results. The first reason is immunosenescence, which is the phenomenon of decreasing immune function with increasing age [44]. Second, the different grouping standards for age can partly explain some of the contradictory results. Third, the ICI types, whether they were used in combination or individually, differed between the treatment and control groups. Moreover, several recently published large trials [39–41] on lung cancer were included in our study, making our conclusions more reliable.
Furthermore, we analyzed the relationship between the efficacy of ICIs and the patients’ ECOG PS. Patients with different ECOG PS scores could benefit from ICIs in different situations. For example, one study showed that patients with an ECOG PS score of 0 benefited more from ICIs than those with an ECOG PS score of 1 [45], but another study reached the opposite conclusion [46]. Therefore, it remains controversial whether differences in ECOG PS scores could affect the anti-tumor efficacy of ICIs in patients with lung cancer. The results of a previous study showed that the OS benefit was not significantly different between patients with a PS score of 0 and those with a PS score of 1–2 treated with ICIs [14]. Likewise, the results of another study showed that no significant difference was noted in patients with different ECOG PS scores (0–1) [8]. However, a meta-analysis of retrospective and prospective studies suggested that caution should be exercised when deciding on administering ICIs to patients with poor PS (score > 2) [47]. Few patients with an ECOG PS score of 2 who received ICIs were included in the examined randomized controlled clinical trials in this meta-analysis. Thus, we analyzed whether patients in the ECOG PS 0 or 1 group could benefit from ICI treatments; interestingly, no difference between these groups was observed. Therefore, ECOG PS should not be the basis for selecting patients for ICI treatment.
Heterogeneity was also observed between studies. The following aspects may be the source of the heterogeneity. Clinical heterogeneity mainly comes from patients in the control group who received different types of anti-cancer drugs (such as chemotherapy, targeted therapies, or ICIs); hence, it may be difficult to distinguish the prognostic effects in the intervention versus the control group in some trials. There have been some studies that used the open-label method, others that used the double-blind method, and others that did not mention the relevant information, which may be sources of methodological heterogeneity. Additionally, the following measures have been applied to address the heterogeneity: (i) The included data were checked again to ensure that all data were correct; (ii) the random-effect model was used to perform calculations with the data; (iii) subgroup and meta-regression analyses were performed to compare summary estimates at the different subgroups and to assess the potential sources of heterogeneity.
Our meta-analysis had several strengths. First, we considered all recently available evidence and included 24 randomized controlled studies focused on the treatment of lung cancer with ICIs published until September 2020. Second, a total of 15,321 patients with OS and PFS data were included in our meta-analysis, and inclusion of such a large number of patients increased the reliability of our results. Third, we strictly grouped patients according to the original age grouping in the literature and did not merge the data of patients with inconsistent ages, thus, obtaining more credible results. Finally, a detailed assessment of the credibility of the evidence was performed to critically appraise the results.
Nevertheless, there were three studies in our analysis that may have caused a bias in the results. One of the studies was a phase 1/2 study update, whereas one did not mention staging; nevertheless, both studies had qualified data and thus, were included in the analysis. Another study reported the HRs of OS and PFS rates for the control versus experimental arms. Then, we recalculated the HR of the experimental arm versus that of the control, as described by Tierney et al. [48]. Besides, publication bias was found with respect to the OS rates among the ECOG groups. The possible reason was that our study included only published works written in English. Furthermore, our analysis had several other limitations. Especially, our report excluded individual patient data and only included published results. Furthermore, there are always missing values in published articles. In addition, some confounding factors, such as the expression of PD-L1, were not included in the analysis because of the presence of inconsistent cut-off values.