My thoughts are that the Harvard study is a little dated at this point. (BTW, so is Walsh's book on this particular topic, in my opinion) The study cites an important study, the one by Stephenson in 2004. That study was updated in 2007. Stephenson has found that subsets of men who were thought not to be candidates for salvage actually can do very well. The nomogram on the MSKCC website about salvage is based on the 2007 study and a correction that had to do with hormone therapy. At the time the Harvard piece was written, Stephenson's earlier article had just come out, and the important good news it carried are underweighted in the article, I think.
As far as the rate of biochemical recurrence after surgery, that sounds right in line with everything else I've read--up to about 30% of men will experience BCR at some point after surgery, but the data includes surgeries from quite a while ago. Walsh, in his 2007 book (p. 372) says: "At last, we have truly long-term results on a large number of men who have been followed for more than 20 years. In all of these patients, the probability of maintaining an undetectable PSA at five, ten, fifteen, and twenty years was 90 percent, 82 percent, 78 percent, and 71 percent, respectively." He goes on to note, however, that because of the longitudinal nature of the study, hundreds of men involved were diagnosed in the pre-PSA era, when cancer was more likely to be diagnosed at later stages. He says that a later study shows that "in men who underwent surgery between 1989 and 1992, it [the freedom from BCR rate] skyrocketed to 80 percent" from the 67 percent BCR-free who had surgery between 1982 and 1988. So yes, IMHO, 15-30% sounds about right, but for people like yourself, the BCR rate is probably pretty low comparatively speaking.
On a personal note, having had biochemical recurrence and undergoing salvage, men like me have a 38% chance of success six years out. Not the greatest of odds, but they beat the alternative had I chosen to not do salvage. If I had based my decision on studies earlier than those of Stephenson's, I might not have been so enthusiastic, since it's easy to find more simplistic predictions like "If your PSA is doubling faster than 10 months, you likely have metastatic disease and should not undergo salvage radiation" or "If your PSA rises within the first year", or even worse "salvage radiation should be performed only when the cancer is confirmed to still be local" etc. We now know that predicting the outcome of salvage radiation is more subtle, and often surprising. For example, Trock, Walsh, Partin, et al. recently found that salvage radiation seems to impart the greatest survival benefit precisely to the men who used to be thought beyond salvage--those whose doubling time was the fastest. (See: Trock BJ, Han M, Freedland SJ, Humphreys EB, DeWeese TL, Partin AW, Walsh PC. Prostate cancer-specific survival following salvage radiotherapy vs observation in men with biochemical recurrence after radical prostatectomy. JAMA. 2008 Jun 18;299(23):2760-9. PubMed PMID: 18560003.) Stephenson has found that a single high risk factor (Gleason 8 or higher, fast doubling time, short time to recurrence, etc) isn't all that important. Now when you start adding them together, it's a different story.
Zen9, looking at your stats in your signature, I would not be overly worried about all of this. Chances are, you won't have a recurrence, and if you do, there will be two questions: 1.) Will you otherwise live long enough for this to bother you? and 2.) Is the cancer likely localized? In the first question, if your PSA starts creeping back 20 years from now, maybe you won't have to anything at all. If you're still young enough to worry about it, salvage RT may offer you a second shot, and speaking for myself, SRT isn't anything to be afraid of.
Just my thoughts! Thanks for bringing this interesting topic up for discussion.
Dx Feb 2006, PSA 9 @age 43
RRP Apr 2006 - Gleason 3+4, T2c, NX MX, pos margins
PSA 5/06 <0.1, 8/06 0.2, 12/06 0.6, 1/07 0.7.
Salvage radiation (IMRT) total dose 70.2 Gy, Jan-Mar 2007@ age 44
PSA 6/07 0.1, 9/07 and thereafter <0.1