51P - Phase 1B (Ph1b), MESOVAX clinical trial of pembrolizumab (P) and dendritic cell vaccine (DCvax) in advanced pleural and peritoneal mesothelioma (M): preliminary results

Background

M is a rare cancer with limited terapeutic options. Immunotherpy has shown hints of activity and, despite combination of immunotherapic agents is the new standard of care for non epithelioid tumors, further study are requested to improve therapeutic strategies. DCvax has shown activity in M with a good safety profile. Our data showed that DCvax induces the expression of PD-L1 on tumor cells. The addition of DC to P may sensitize patients to the effects of PD-1 blockade.

Methods

MESOVAX is a Ph1b study evaluating safety of P 200 mg Q3W and an autologous DCvax administered subcutaneously Q3W for a maximum of 6 cycles, in pretreated metastatic M patients (pts). Primary endpoint was safety; secondary were PD-L1 expression variations defined by immunohistochemistry (IHC) and efficacy (objective response rate [ORR], duration of response [DOR], progression-free survival [PFS], overall survival [OS]).

Results

As of 30 Aug 2023, 6 pts (median follow-up 20.1 mo) were treated and evaluable for safety pre-planned interim analysis. Median age was 64 yrs, all pts were male, 17%/83% were ECOG PS 0/1. All pts had epithelioid M. Any grade treatment-related adverse events (TRAEs) occurred in 5 pts (83%); most common were local reaction to injection site (4 pts, 67%), asthenia (2 pts, 33%) and fever (2 pts, 33%). None of the patients experienced grade 3–4 TRAEs. Concerning the treatment, 4 pts (67%) received 6 cycles of P+DC; 3 received maintenance P. In a preliminary analysis of tumor response, at the first planned evaluation (median treatment duration 2.1 mo),2 had SD, 1 had PR and 3 had PD. PD-L1 expression at baseline and at week 12 is summarized on Table. Table: 51P

PD-L1 expression defined by IHC at screening and at week 12

Legend: ND: not done; NE: not evaluable.

Conclusions

Preliminary results of MESOVAX trial of P combined with DC showed a manageable toxicity and demonstrated encouraging preliminary efficacy. The trial is actively recruiting.

Clinical trial identification

EudraCT 2018-000500-42.

Legal entity responsible for the study

The authors.

Funding

Merck MSD.

Disclosure

F. De Rosa: Financial Interests, Personal, Speaker, Consultant, Advisor: MSD, Pierre Fabre, Novartis, Sun Pharma. All other authors have declared no conflicts of interest.