VIDEO: CYCLONE 2 probes abemaciclib and abiraterone in prostate cancer

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So CYCLONE 2 was a study looking at abemaciclib with abiraterone in patients with metastatic castration-resistant prostate cancer. So as many are familiar, abemaciclib, that's a CDK4/6 inhibitor used most often in metastatic, hormone-positive breast cancer, and AR signaling, androgen receptor signaling, is thought to activate CDK4/6 to sustain proliferation of prostate cancer cells.

So the idea here was that combining abemaciclib with abiraterone might have a synergistic effect at overcoming some resistance pathways. CYCLONE 2 was a phase three study that looked at that combination, and unfortunately did not meet its primary endpoint of RPFS. The combination arm only achieved about 22 months compared to 20 months of placebo plus abiraterone, and hazard ratio was 0.83 with a non-significant P value, and overall survival was approximately the same. There's a trend towards improvement in the combination arm at 38 per months versus 33, but not statistically significant.

Toxicity was substantially higher in the combination arm, not surprisingly, with things like diarrhea, cytopenia, and fat toxicity being quite pronounced. We'll have to wait for cycle three to see if this combination has any value in the high-risk, hormone-sensitive setting. But given the results of CYCLONE 2, I don't anticipate there'll be new signals of efficacy.