This is the first trial to evaluate the effect of M-PHP combined with ipilimumab and nivolumab in UM patients. The MTD of the combination treatment will be defined in phase Ib. Subsequently, the efficacy of the combination of M-PHP and ICI will be compared to M-PHP only in a randomized phase II trial.
ICI revolutionized the treatment of patients with CM in the past years. Treatment with ICI relies on activation of antigen-specific T-cells by inhibiting their normal immunoregulatory mechanisms (12, 26). Updated survival data from the Checkmate 067 trial after a minimum follow-up of 5 years showed the supremacy of nivolumab either alone or in combination with ipilimumab over ipilimumab monotherapy in CM. The five-year OS was 52% in patients that were treated with ipilimumab plus nivolumab, compared to 44% and 26% in the nivolumab only and ipilimumab only groups respectively (27). Several studies evaluated the effect of anti-CTLA-4 and anti-PD-1 monoclonal antibodies in CM patients (2, 9–11, 26), but results of ICI in patients with UM have been disappointing. Possible reasons for the lower response rates of ICI in metastatic UM may include the low mutational burden and therefore the limited expression of neoantigens recognizable by cytotoxic T-cells. One explanation for this difference is the lack of ultraviolet-radiation damage in UM, when compared to CM (12). Additionally, only about 10% of UM primary tumors (28) and 5% of the UM cells in metastatic disease express PD-L1 (29). Another factor is that UM arises in an immune-privileged environment, that possesses inhibitory properties against both the innate and the adaptive immune system (30). Finally, it is postulated that the liver functions as an immune-modulating organ, possibly enhancing tolerance to tumor antigens (2, 31). To improve efficacy of ICI, broadening of the T-cell repertoire is necessary. Combining ipilimumab and nivolumab might overcome the need for a high mutational load (32). Recent studies confirm that combination treatment shows higher response rates than single-agent treatment with either PD-1 or CTLA-4 inhibitors alone in UM patients. A recent large retrospective trial including both pre-treated and treatment-naïve patients with metastatic uveal melanoma showed an ORR of 11.6% and disease control rate of 36.0% (median OS of 15 months) (14). These results were comparable with those of a phase II trial, with an ORR of 18% and clinical benefit rate of 37% (median OS 19.1 months) (15). In the GEM-1402 study, a phase II trial conducted on treatment-naïve metastatic UM patients, a similar objective response rate of 11.5% was found, with a higher disease control rate of 63.5% and a median OS of 12.7 months. Interestingly, in this trial patients with extrahepatic disease showed a longer survival than patients with metastases located in the liver (23.5 months compared to 9.2 months). Even though this difference was not statistically significant, it suggests that patients with extrahepatic disease could better benefit from combination treatment with ipilimumab and nivolumab compared to those with hepatic metastases (16).
As the liver is the dominant predilection site for UM metastases and survival correlates with disease control in the liver, a variety of liver-directed therapies have been studied. While published literature varies considerably in terms of patient selection, disease extent, design and outcome measurements, it suggests that locoregional liver therapies offer survival benefit in selected patients with hepatic metastases (33–36).
Locoregional therapies may induce immune responses and trials are trying to exploit the potential synergistic effect of combined local liver therapy with ICI in melanoma patients. However, the number of studies investigating such combination therapy in UM is limited up until now. A retrospective study evaluated a combination treatment of transarterial radioembolizaton (TARE) with CTLA-4 or PD-1 antibody therapy showed promising results. The study demonstrated a median hepatic PFS of 15.0 months and OS of 17.0 months after start of TARE, with a local disease control rate of 63.6%. However, no standard treatment regimen was applied and study sample size was small (37). A recent prospective, phase Ib/II trial showed that combining radio-frequency ablation (RFA) with ipilimumab 3 mg/kg was well tolerated by patients. This resulted nonetheless in very limited clinical activity, measured by a low disease control rate of 7%, a six-month PFS of 7% and a one- and two-year OS of 51% and 7%, respectively (38). A phase II trial combining ipilimumab and nivolumab with immuno-embolization in metastatic UM patients is on-going (recruiting, trial number NCT03472586).
In the present trial we are combining M-PHP with ICI. M-PHP has become the standard of care in our institution, showing safe and favorable outcomes in patients with hepatic metastases of UM (39, 40). The principle of M-PHP is to isolate the venous return of the liver from the systemic circulation. The blood returning from the liver is purified from melphalan via an extracorporeal circuit and returned to the patient. This allows perfusion of the liver with a very high dose of melphalan, which would be toxic and would lead to severe complications when administered systemically. The superiority of M-PHP over best alternative care has been demonstrated in a randomized controlled multicenter phase III trial for patients with liver metastases from CM and UM (18). In this trial the hepatic PFS and OS in the M-PHP group were 7.0 and 5.4 months respectively, compared to 1.6 and 1.6 months respectively in the best alternative care group. In a prospective, phase II trial including 35 patients with UM metastases confined to the liver, we found a 72% objective response rate after M-PHP and a median OS of 19.1 month (19). A recent retrospective study on M-PHP in 51 patients with metastatic UM demonstrated a slightly lower median OS of 15.3 months. However, this study also included patients with limited extrahepatic metastases, which could explain the difference (20). To date little is known on immunomodulation by M-PHP. Therefore, exploratory end-points are included in our study; immunological parameters, and changes in tumor immune-infiltrates, PBMC and serum.