PembROlizuMab Immunotherapy Versus Standard Chemotherapy for Advanced prE-treated Malignant Pleural Mesothelioma

Mesothelioma is an aggressive malignancy usually affecting the surfaces of body coelomic cavities. It most commonly originates from the pleura with a propensity to the lower parietal pleura and costo-diaphragmatic recess, and is almost always caused by asbestos exposure, with a usual lag time of 30 years between exposure and presentation. Outcomes for most patients are invariably fatal, with median survival from presentation around 9-12 months in most series due to difficulties in achieving a complete microscopic surgical resection and tumour relative chemo-refractoriness. Whilst initially considered rare, due to the demand of asbestos of all varieties associated with industrialization following the Second World War, the background incidence of mesothelioma of 1/million has risen to 40/million in some countries. In the UK, where substantial asbestos exposure continued until the 1970s, the death rate is the highest in the world with a current epidemic of new cases, predicted to continue for another 5-10 years. Two main histological subtypes of mesothelioma are identified. The epitheliod subtype is the commonest, accounting for around 40% of cases, whilst the sarcomatoid subtype is observed in 20% of cases; the latter being typically aggressive and chemorefractory. Around 35% cases have features of both epitheliod and sarcomatoid subtypes and are termed biphasic subtype.

For patients with pleural mesothelioma, in whom surgery is not considered appropriate, systemic chemotherapy (platinum combined with pemetrexed) remains the international standard of care. Cisplatin/pemetrexed is associated with a response rate of 41% and confers an OS advantage of 3 months over cisplatin alone, and is the only licensed systemic therapy for mesothelioma in Europe. Despite this, the median survival is 9-12 months from most series in unresectable cases. At relapse, after platinum-based chemotherapy, no anti-cancer systemic therapies are licensed. Whilst several small phase II studies and retrospective series have suggested potential efficacy for chemotherapy with agents including carboplatin/gemcitabine, or vinorelbine, none thus far have demonstrated efficacy benefit in a randomised study, with median PFS rates reported of about 3 months for both gemcitabine and vinorelbine. There is therefore a huge unmet need for effective therapy for patients with relapsed pleural mesothelioma. The largest trial ever performed of systemic therapy in relapsed pleural mesothelioma in 661 patients documented the natural outcome of this group of relapsed mesothelioma patients, reporting a median OS of 27.1 weeks (6 months) and median PFS for 6.1 weeks (1.5 months) for placebo.

Programmed cell death-1 (PD-1) is a co-inhibitory molecule at the immunological synapse that acts as a major regulator of adaptive immunity, and is exploited by tumour cells to result in adaptive immune resistance (tolerance). This occurs when PD-1 binds to the ligands PD-L1 (B7H1) or PD-L2, which are expressed on many tumour types. High PD-L1 expression on tumours is associated with poorer outcomes. Mesothelioma has been shown to express PD-L1, with a small study identifying PDL1 expression in up to 40% of mesotheliomas. Moreover, immunologically-mediated inflammation is known to be a key driver for mesothelioma development via the Nalp3 imflammasome.

Pembrolizumab (MK-3475) is a potent and highly selective humanized monoclonal antibody (mAb) of the IgG4/kappa isotype designed to directly block the interaction between PD-1 and its ligands, PD-L1 and PD-L2.

There is a need to identify new ways for the systemic therapy of malignant mesothelioma and immune checkpoint inhibition is a promising way forward. Results from the proposed trial will contribute to overcoming tumour-specific immune suppression with immune checkpoint inhibition.

Inclusion criteria

• Histologically confirmed malignant pleural mesothelioma (all subtypes are eligible)
• Progressing after or on previous platinum based chemotherapy.
• Availability of tumour tissue for translational research.
• Female and male patients aged 18 years or over.
• Eastern Cooperative Oncology Group (ECOG) performance status 0-1.
• Life expectancy of at least 3 months.
• Measurable or evaluable disease according to RECIST 1.1 criteria.
• Adequate renal function
• Creatinine 1.5 × Upper Limit of Normal (ULN) OR Calculated creatinine clearance 40 mL/min (using the Cockroft-Gault formula).
• Adequate haematological function
• Haemoglobin 90 g/L or 5.6 mmol/L
• White Blood Cell (WBC) 1.0 × 109/L
• Lymphocytes 0.5 g/L
• Absolute neutrophils count (ANC) 1.5 × 109/L
• Platelet count 100 × 109/L.
• Adequate liver function
• ALT and AST 2.5 × ULN. If the patient has liver metastases, ALT and AST must be ≤5 × ULN.
• Women of childbearing potential, including women who had their last menstrual period in the last 2 years, must have a negative serum or urine pregnancy test within 35 days before randomisation (the test has to be repeated 72 hours before pembrolizumab treatment start).
• Written informed consent must be signed and dated by the patient and the investigator prior to any trial-related intervention including the submission of mandatory biomaterial.

Exclusion criteria

• Prior therapy with an anti-programmed cell death protein 1 (anti-PD-1), anti-programmed cell death ligand 1 (anti-PD-L1), anti-programmed cell death ligand 2 (anti-PD-L2), anti-CD137, or anti-cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) antibody (including ipilimumab or any other antibody or drug specifically targeting T-cell co-stimulation or checkpoint pathways).
• Prior therapy with gemcitabine or vinorelbine.
• Known active central nervous system metastases and/or carcinomatous meningitis. Patients with previously treated brain metastases may participate provided they are stable (without evidence of progression by imaging for at least 4 weeks prior to randomisation and any neurologic symptoms have returned to baseline), have no evidence of new or enlarging brain metastases, and are not using steroids for at least 7 days prior to randomisation. This exception does not include carcinomatous meningitis, which is excluded regardless of clinical stability.
• Known or suspected hypersensitivity to pembrolizumab or any of its excipients.
• Known unstable or unresolved surgical or chemotherapy-related toxicity that would compromise the patient's capacity to participate in the trial.
• Previous allogeneic tissue/solid organ transplant.
• Live vaccines within 30 days prior to first dose of pembrolizumab.
• Regular intake of immune-modulating drugs (such as interferon, methotrexate).
• History of (non-infectious) pneumonitis that required steroids, evidence of interstitial lung disease or active, non-infectious pneumonitis.
• Active autoimmune disease that has required systemic treatment in the past 2 years (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive drugs). Replacement therapy (i.e. thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) or topical therapy (e.g., steroids) for psoriasis or eczema is not considered a form of systemic treatment.
• Ongoing clinically serious infections requiring systemic antibiotic or antiviral, antimicrobial, or antifungal therapy.
• Human immunodeficiency virus (HIV) infection.
• Known active hepatitis B or hepatitis C.
• Known history of active tuberculosis.
• Patients with diagnosed immunodeficiency or receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to randomisation.
• Patients with other serious diseases or clinical conditions, including but not limited to uncontrolled active infection and any other serious underlying medical condition that could affect the patient's capacity to participate in the trial.
• Substance abuse, medical, psychological or social conditions that may interfere with the patient's participation in the trial or evaluation of the trial results.
• Women who are pregnant or in the period of lactation.
• Sexually active men and women of childbearing potential who are not willing to use an effective contraceptive method during the trial and up to 120 days following cessation of trial treatment.