To our knowledge, there has been so far no meta-analysis that evaluated the efficacy and safety of ADC plus ICI in cancer patients. Quhal [33] and Ulas [34] merely compared the efficacy of ICI-based therapy without referring to ADC, and another meta-analysis compared dual ICI with ICI monotherapy [35]. Besides, Zhang et al. presented the first meta-analysis that evaluated efficacy and safety of ADC [36]. But our current meta-analysis revealed satisfactory ORR and acceptable irAEs after statistical analysis of individual data of 551 patients from 11 clinical trials. The results showed that the cumulative prevalence of total ORR was up to 0.59 (95% CI 0.45–0.72) when treated with novel ADC plus ICI, and the AEs were mainly digestive and skin problems.
Subsequent clinical studies had been constantly carried out to evaluate the efficacy of ADC plus ICI, and most results validated some of the efficacy benefits of the product. However, some follow-up data from late-stage clinicals didn’t show effectiveness when compared with conventional chemotherapy drugs. For example, in the KATE-2 study, there is no significant PFS difference between T-DM1 and T-DM1 plus atezolizumab in HER2-positive BC patients according to intention to treat (ITT). Nevertheless, survival benefir was observed in PD-L1-positive subgroup with a median PFS of 8.5 vs 4·1 months (HR 0.60 95% CI, 0.32–1.11). Undeniably, patients failed to gain benefit from the combination therapy. It may be explained by lagging immune status and previous multiple lines of therapy. But on the other hand, the PD-L1 and HER2 positive patients showed a trend towards better survival benefits, which highlighted the importance of finding suitable ITT and treatment strategy based on gene detection. It is also worth noting that NCT0444886 and NCT04740918 were expected to kindle hope for precise treatment by offering more worthy evidence .
Further analysis suggested that the improvement in patients with combination therapy may show subgroup-level differences, which was correlate with information on histotype and regimens. It is clear that cHL benefited most from combinations, UC ranked second, followed by PMBL, BC, NSCLC and collection of several advanced solid tumors. Consequently, we inferred that it may be related to the drug target. Tumors with high expression of targeted antigen showed better effect when treated with ADC [37, 38] or ICI. CD30 and PD-L1 is consistently overexpressed in patients with HL [39] [40] and significant inflammatory cell infiltration was detected in tumor samples. Interestingly, PMBL, a rare but aggressive NHL, was also characterized by high expression of PD1 and CD30. From this we could speculate that Nivolumab and Pembrolizumab, anti–PD-1 immune checkpoint inhibitor, and brentuximab vedotin (BV), an anti-CD30 antibody–drug conjugate, may have synergistic activity. It has been proved that human epidermal growth factor 2 (HER2) was highly expressed in multiply solid tumors including BC, GC, UC and NSCLC [41, 42] (ordered based on the expression), with protein overexpression, gene amplification, mutation and etc. People also found that HER2-positive oncogenesis was more likely to be correlated to higher PD-L1 and immunogenicity [43], which suggested that HER2-high tumors may benefit more from ADC + ICI therapy. This may testified the ORR results of our subgroup based on histotype as well. As for why hematologic malignancy could better benefit from ADC + ICI, we supposed it may be related to the more complex tumor microenvironment of solid tumors [44]. However, we should also be cautious to make this inference for relevant researches are still in a relatively preliminary state, and HER2-low tumor is a field remaining to be explored for combinations [45].
As for the subgroup analysis based on regimens, since pairing ADC with ICI is a relatively new strategy, and many clinical trials exploring this dynamic field are still ongoing or in phase I/II stages, exaggerated efficacy evalution and data insufficience should be considered when comparing the different combinations. In our study, both BV + Nivo and BV + Pembro used for HM seemed to bring more ORR benefits than the rest arms, which could be explained by heterogeneity caused by tumor types mentioned above. When comparing the efficacy between BV + Nivo and BV + Pembro, we could not conclude which combination was better, given that both Pembro and Nivo were targeting PD-1 inhibitors whereas the totality of efficacy data were still not uniformly reported. Moreover, other ongoing clinical trails on combinations of BV + PD-1 inhibitor such as BV + Ipilimumab (NCT01896999) may also contribute to the selection and formulation of treatment plan for biomarker-based rationale drugs. Besides, we found EV (targeting Nectin-4) + Pembro could benefit UC patients more, compared with SG (targeting Trop-2) + Pembro. However, we should take a rational view of these data in case of other factors interfering with this results. For example, the differences in the baseline characteristics for patients in SG group experienced previous more than third-line therapy while patients in EV group didn't received therapy for locally advanced or metastatic UC. As for T-DM1 + Atezo therapy, the survival benefit of BC patient in the combination arm failed to show significant improvement when compared with the control arm. Therefore, further evaluation was still needed before the evidence was translated into reliable survival outcomes. As for other treatment schemes, the data of relevant studies are still needed to support clear comparative judgment. Anyway, as the selectivity and accessibility of ADC plus ICI demonstrated a biomarker-based rationale that was associated with efficacy of combinations, it is important to recognize that inter- and intra-tumor heterogeneity should be fully considered [46]. For more satisfactory risk-benefit profiles, new strategy of optimal combinations to maximize the advantages of them is something we require to work out.
As for safety analysis, emerging combinations are seen as a game-changer when the efficacy of monotherapy is limited, but it can act as a double-edged sword if the combinations induce more observed AEs. The irAEs identified in our study were mainly digestive and skin problems, and no severe AEs were spotted. In general, the toxicity of ADC therapy is mainly related to the cytotoxic drugs carried, including hematotoxicity, neurotoxicity, hepatotoxicity and so on [47], with regards to dosing, drug design, or off-target binding [48]. Besides, toxicity of ICI may have delayed onset and prolonged duration, from mild skin diseases to severe gastrointestinal tract reactions to life-threatening myocarditis, cheifly affecting skin, gastrointestinal, endocrine, lung and muscle tissue [49, 50]. Even worse, the superposition of this two toxicities may offset the potential therapeutic benefits. Fortunately, the early data from combination studies of ADC and ICI have not revealed significant additive toxicity so far, which were consistent with the results of our study. And in order to timely alleviate or improve the influence from this combinations, such as interruption or drug reduction, measures should be taken to relieve their symptoms. Additionally, Advanced assessment for patients’ physical condition is essential, especially for those at high risk. Once the AEs happened, clinical nursing, temporary dose interruption and/or dose reduction should be considered.
The following limitations merit consideration. For a lack of placebo arm, the efficacy of combinations may be exaggerated, and further control group are in demand to minimize the placebo effect. Furthermore, in our meta-analysis, the tumor type, disease progression and different drug mechanism may have biased the results. Although we have performed subgroup analysis to reduce this bias, some partial trials were still unable to be reassessed because of limited sample data. Last but not least, although the reasons for drug efficacy and specific benefit from specific caner type have been evaluated from antigen and target levels, our study still remained on the interpretation of phenomena, and further mechanism researches are needed.