Time off treatment in IAD: Still hard to predict

"All of these men had a rising PSA only, but those with a short doubling time and high-grade disease look exactly as though they had clinically apparent metastatic prostate cancer with 5-year, 50% survival and 1% survival at 10 years," Dr. Klotz explained.

The great diversity of patients in this study is typical of problems presented by study data in this area, he pointed out.

"We have patients here for whom quality of life is paramount. They have probably been over-treated with hormones, and we need to think about how to reduce the impact of androgen deprivation. Is even intermittent therapy required for these patients? That is one of the controversies," he said.

A Canadian study of 100 prostate cancer patients that was started in the early 1990s, when PSA became available for regular use, enrolled men with PSA levels of approximately 20.0 ng/mL, a higher level than would be acceptable today, said Dr. Klotz. In the intermittent group, PSA was normalized at 24 and 32 weeks, and therapy was stopped at 36 weeks.

"The baseline PSA levels of 4.0 ng/mL to 10.0 ng/mL were clearly predictive of the off-treatment interval, and [the patients] were almost 2 years off treatment," Dr. Klotz said.

The PSA nadir was a function of baseline PSA, falling to 95% of the baseline measurements.

"This was interesting: The lower the PSA at the start, the lower the PSA nadir. What this also meant was the magnitude of the PSA response was very consistent," Dr. Klotz explained.