Pembrolizumab Active in Thymic Carcinoma


Key Points

  • Response was observed in 22.5% of patients, including six of 10 with high PD-L1 expression.
  • Severe autoimmune toxicity occurred in 15% of patients.

In a single-center phase II study reported in The Lancet Oncology, Giaccone et al found that pembrolizumab (Keytruda) produced durable responses in patients with recurrent thymic carcinoma.

Study Details

In the study, 40 evaluable patients with advanced disease progressing after at least one line of chemotherapy at Lombardi Comprehensive Cancer Center were enrolled between March 2015 and December 2016 and treated with pembrolizumab 200 mg every 3 weeks for up to 2 years. The primary endpoint was the proportion of patients achieving response based on RECISTv1.1 criteria.

Response Rates

Median follow-up was 20 months. Response was observed in nine patients (22.5%)—including complete response in one—and stable disease was observed in an additional 21 (53%). Data on programmed cell death-ligand 1 (PD-L1) expression was available for 37 patients. In 10 patients with ≥ 50% staining in tumor cells (high expression), response was observed in 6 (P = .005 vs response rate in 27 patients with lower PD-L1 expression). Median duration of response was 22.4 months; 8 patients had stable disease ≥ 6 months and 3 for ≥ 1 year. In post-hoc analysis, progression-free (median = 24 vs 2.9 months) and overall survival (median = not reached vs 15.5 months) were longer in patients with higher vs lower PD-L1 expression.

Adverse Events

The most common grade 3 or 4 adverse events were increased AST and ALT (13% each), dyspnea (8%), myalgia/myositis (8%), and increased creatine phosphokinase (8%). Severe autoimmune toxicity occurred in six patients (15%), including myocarditis in two (5%). No deaths due to toxicity were reported.

The investigators concluded, “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.”

The study was funded by Merck & Co.

Giuseppe Giaccone, MD, of Lombardi Comprehensive Cancer Center, Georgetown University, is the corresponding author for The Lancet Oncology article. 

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.