Pembrolizumab in patients with thymic carcinoma: a single-arm, single-centre, phase 2 study

Abstract

Background: Treatment options are limited for patients with thymic carcinoma. These aggressive tumours are not typically associated with paraneoplastic autoimmune disorders, and strong PD-L1 expression has been reported in thymic epithelial tumours. We aimed to assess the activity of pembrolizumab, a monoclonal antibody that targets PD-1, in patients with advanced thymic carcinoma.

Methods: We completed a single-arm phase 2 study of pembrolizumab in patients with recurrent thymic carcinoma who had progressed after at least one line of chemotherapy. This was a single-centre study performed at Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, USA. Key inclusion criteria were an Eastern Cooperative Oncology Group performance status of 0-2, no history of autoimmune disease or other malignancy requiring treatment or laboratory abnormality, and adequate organ function. Patients received 200 mg of pembrolizumab every 3 weeks for up to 2 years. The primary objective of the study was the proportion of patients who had achieved a response assessed with Response Evaluation Criteria in Solid Tumors version 1.1. Analysis was per protocol, in all eligible patients. The study is registered with ClinicalTrials.gov, number NCT02364076, and is closed to accrual; we report the final analysis.

Findings: 41 patients were enrolled from March 12, 2015, to Dec 16, 2016, of whom 40 were eligible and evaluable and one was excluded because of elevated liver enzymes at screening. The median follow-up was 20 months (IQR 14-26). The proportion of patients who achieved a response was 22·5% (95% CI 10·8-38·5); one (3%) patient achieved a complete response, eight (20%) patients achieved partial responses, and 21 (53%) patients achieved stable disease. The most common grade 3 or 4 adverse events were increased aspartate aminotransferase and alanine aminotransferase (five [13%] patients each). Six (15%) patients developed severe autoimmune toxicity, including two (5%) patients with myocarditis. There were 17 deaths at the time of analysis, but no deaths due to toxicity.

Interpretation: Pembrolizumab is a promising treatment option in patients with thymic carcinoma. Because severe autoimmune disorders are more frequent in thymic carcinoma than in other tumour types, careful monitoring is essential.

Funding: Merck & Co.

Figure 1:. Overall response

(A) Waterfall plot of the best response in all eligible patients. *Patients have an ongoing response or stable disease. (B) Measurements of target lesions at each timepoint in all eligible patients (where CT scans were taken every two cycles, which represents 6 weeks). (C) Duration of treatment. With a few exceptions, treatment cycles were repeated every 3 weeks. The arrows indicate that patients are either still on treatment, are still in follow-up after completing 2 years of therapy (35 cycles), or, in the case of patient number 28, were taken off the study but are still responding.

Figure 2:. Progression-free survival (A) and overall survival (B).

Grey highlighting represents 95% CIs.

Figure 3:. PD-L1 expression and response to pembrolizumab.

Error bars are SD. Horizontal lines are medians.