Adding Keytruda to a Combination of Abiraterone Acetate Plus Prednisone Continues to Demonstrate Anti-Tumor Activity in a Group of Patients With Prostate Cancer

With nearly one-year of additional follow-up, adding Keytruda to the combination of abiraterone acetate and the steroid prednisone shows continued benefit in men with metastatic castration-resistant prostate cancer.

Adding Keytruda (pembrolizumab) to abiraterone acetate and the steroid prednisone was shown to produce anti-tumor activity in patients with metastatic castration-resistant prostate cancer who had not previously received chemotherapy for their cancer, according to recent study findings.

The results, which were simultaneously published in the Annals of Oncology, werepresented at the 2022 European Society for Medical Oncology Congress.

Prostate cancer is considered “castration-resistant” if the disease has progressed after androgen deprivation therapy, which is an effort to lower testosterone levels through surgery or medication, has been completed. This may describe disease progression or the development of new metastases. Approximately 10% to 20% of patients with prostate cancer are castration-resistant.

The current standard of care for castration-resistant prostate cancer has been the use of abiraterone acetate plus the steroid prednisone. Here, Dr. Mark Linch, a consultant medical oncologist at University College London Hospitals, and colleagues examined the safety and effectiveness of adding Keytruda to the combination of abiraterone acetate and prednisone.

Out of the 103 patients enrolled onto the trial and treated with the Keytruda-based regimen, 56.3% achieved a confirmed prostate-specific antigen response (a protein made by the prostate found in blood). Moreover, 81 patients (78.6%) experienced a prostate-specific antigen reduction from baseline, suggesting the efficacy and safety of adding Keytruda to abiraterone acetate and the steroid prednisone.

For patients with RECIST-measurable disease, the overall response rate (percentage of patients whose disease fully or partially responds to treatment) was 16.2%.

According to the National Cancer Institute, RECIST is a standard way that health care providers measure how well a patient with cancer’s disease responds to treatment. It is based on whether tumors shrink, stay the same or get bigger.

One of the patients achieved a complete response, while five achieved partial response. The overall response rate in patients not treated with next-generation hormonal agents was 21.7%, and 7.7% for those who were not treated with Xtandi (enzalutamide).

Two patients with RECIST non-measurable disease achieved a complete response.

The disease control rate (the proportion of patients in whom the best overall response is determined as complete response, partial response or stable disease) among all 103 patients. The disease control rate was 58.7% in patients with no prior treatment with next-generation hormonal agents and 7.4% in patients who had been treated with Xtandi.

As of Feb. 2022, which was the last time the investigators reviewed the findings, the median overall survival (time from first treatment to death from any cause) among the entire patient population was 29.7 months. Approximately half (49.5%) of the patients were alive at 36 months The findings showed that a median duration of response (time from randomization to disease progression or death in patients whose disease achieved a complete or partial response to treatment) was not yet reached.

Treatment-related side effects occurred in 90.3% of patients, with 36.9% experiencing a serious, severe or fatal side effect. Five patients died due to side effects, with one being treatment-related muscle weakness.

To be eligible for enrollment onto the trial, patients diagnosed with castration-resistant prostate cancer had to have received no prior chemotherapy or were intolerant to or had disease progression while receiving Xtandi, a nonsteroidal antiandrogen. Patients enrolled in the initial trial displayed disease progression at or before six months of screenings and had an Eastern Cooperative Oncology Group Performance Status of 0 to 1. Of note, this is used to assess the functionality of a patient. A score of 0 to 1 indicates that an individual is mostly self-sufficient and can do daily tasks on their own.

“With an additional 10.6 months of follow-up, (Keytruda) plus abiraterone acetate and prednisone continued to show antitumor activity and acceptable safety in patients with chemotherapy-naive (metastatic castration resistant prostate cancer),” the investigators wrote in an abstract of the data.

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