Finasteride, which remains a controversial drug in the treatment of men with advanced prostate cancer, prolongs the time of off-treatment in men with advanced prostate cancer when they are using intermittent androgen suppression therapy (IAD). One of the questions not yet understood is whether this results from a true increase in prostate-specific antigen (PSA) doubling time or instead is reflective of a delay in PSA responsiveness to regained testosterone production.

Researchers at The Prostate Center at Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada, attempted to distinguish between these two possibilities and consider how the effectiveness of finasteride might be altered if androgens are synthesized within the malignant cell rather than the testis.

This was a very small study of only six men who were followed on IAD for intervals ranging from 7 to 10 years. The effects of finasteride on the length of the off-treatment period in at least one cycle in each man was measured with monthly determinations of serum PSA and testosterone and calculation of PSA doubling time using linear regression analysis.

They concluded that:

* The administration of finasteride was associated with a reduction in the rate of increase of serum PSA in the off-treatment period of any given cycle within a sequence of 5.

*In a total of 15 cycles, finasteride extended PSA doubling time from a mean of 7.7 weeks (n = 11, range 2.3-29.8 weeks) to a mean of 45.1 weeks (n = 6, range 13.8-99.7 weeks).

However, one man was characterized by an apparent pseudo-resistance to finasteride in the 2nd cycle of treatment and another man by complete resistance to finasteride in the 4th cycle.
They found that Finasteride can be introduced into any cycle of intermittent androgen suppression with the expectation of an extension of PSA doubling time.

The small sample size in this study means that one has to be cautious when generalizing to the general population. However, their results are consistent with many men informally report.
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Can J Urol. 2010 Jun;17(3):5162-9; Locke JA, Bruchovsky N

PubMed Abstract
PMID: 20566007

Joel T Nowak, MA, MSW