Ipilimumab ± radiation therapy in men with mCRPC

Final data have just been reported on the results of a Phase I/II study of treatment with ipilimumab as monotherapy and in combination with radiotherapy in men with metastatic, castration-resistant prostate cancer (mCRPC).

Slovin et el. have provided data on fewer than 100 patients in an article in Annals of Oncology.

Here is a brief summary of the available data:

  • In dose escalation, 33 patients received ipilimumab every 3 weeks × 4 doses at 3, 5, or 10 mg/kg or at 3 or 10 mg/kg + radiotherapy (8 Gy/lesion) in the Phase I dose escalation study.
  • The 10-mg/kg cohorts were expanded to 50 patients.
    • 16 patients were treated with ipilimumab monotherapy.
    • 34 patients were treated with ipilimumab + radiotherapy.
  • Among the 50 patients receiving 10 mg/kg ± radiotherapy,
    • 8/50 patients (16 percent) had PSA declines of ≥ 50 percent (with a duration of  3 to 13+ months).
    • 1/50 patients (2 percent) had a complete response (with a duration of 11.3+ months).
    • 6/50 patients (12 percent) had stable disease (with a duration of  2.8 to 6.1 months).
    • Common immune-related adverse events (irAEs) included
      • Diarrhea (in 54 percent or 27/50 patients)
      • Colitis (in 22 percent or 11/50 patients)
      • Rashes (in 32 percent or 16/50 patients)
      • Pruritus (in 20 percent or 10/50 patients)
    • Grade 3/4 irAEs included
      • Colitis (in 16 percent or 8/50 patients)
      • Hepatitis (in 10 percent or 5/50 patients)
    • There was one treatment-related death reported (in a man receiving ipilimumab at 5 mg/kg) group) occurred.

The authors conclude that, “In mCRPC patients, ipilimumab 10 mg/kg ± radiotherapy suggested clinical antitumor activity with disease control and manageable [adverse events].” However, it has to be said that the degree of disease control appears to have been limited, and the adverse events were significant.

Ipilimumab is currently being tested in several other clinical trials for the treatment of prostate cancer, including a fully enrolled Phase III trial in men with chemotherapy-naive mCRPC and a second fully enrolled Phase III trial in men with mCRPC regardless of whether they had received chemotherapy or not.

Clearly we are going to have to wait to see whether the benefits of ipilimumab in these trials are able to outweigh the risk of complications and side effects.

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