#mcrpc

There has been evidence that the effectiveness of Abiraterone Acetate (Zytiga) along with prednisone (P) can be extended by switching the P to another steroid, dexamethasone (D) in certain men who are castrate resistant and still without symptoms and who start experiencing a rise in their PSA scores. 

Ninety-three (93) men treated with Zytiga + P who experienced biochemical progression (rise in their PSA while still taking Zytiga + P) were switched from 10 mg/day of P to 0.5 mg/day of D until they experienced radiological and/or clinical progression in order to evaluate the effectiveness of substituting the P with D.

The primary endpoint of the study was progression-free survival (PFS).

Results

The median time to PSA progression (the time at which PSA scores increased despite taking Zytiga +P) was 8.94 months. The median PFS on Zytiga +D and Zytiga+corticosteroids (P then D) was 10.35 and 20.07 months. 

A total of 56.25% of men showed a decrease or stabilization in their PSA levels after the switch. The researchers then wanted to understand which men who made the switch from P to D had the best response.

In univariate analysis, three markers of switch efficiency were significantly associated with a longer PFS from the switch: long hormone‐sensitivity duration (≥5 years; median PFS 16.62 vs. 4.17 months,); low PSA level at the time of switch (<50 ng/mL; median PFS 15.21 vs. 3.86 months; and a short time to PSA progression on Zytiga+P (<6 months; median PFS 28.02 vs. 6.65 months). 

In multivariate analysis, hormone sensitivity duration and PSA level were independent prognostic factors.

Conclusion

A steroid switch from P to D appears to be a safe and non‐expensive way of obtaining long‐term responses to Zytiga in selected men with mCRPC. A longer PFS has been observed in men with previous long hormone sensitivity duration, and/or low PSA level and/or short time to PSA progression on Zytiga+P.