How accurate is the Strum model of PSA leakage?

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Veteran Member

Date Joined Aug 2010
Total Posts : 644
   Posted 2/16/2011 4:30 AM (GMT -6)   
Hi -

Does anyone have a sense of how accurate the Strum model for PSA leakage is, and how to interpret discrepancies?

My situation (after RP):

A 40 cc prostate
Gleason 3+4 (25% was G4, 75% was G3)
Tumor volume 3 cc (7.5% of prostate volume)
PSA pre-op was 5.6 tested just a few days before the surgery.

According to the model, PSA should be as follows:
37 cc of health prostate tissue should generate abut 2.5 nl of PSA
2.25 cc of gleason 3 should generate about 9.6 nl of PSA
.75 cc of gleason 4 should generate about 1.5 nl of PSA
so total PSA should be about 13.6, but it was actually 5.6 (measured just a few days before the operation)

So this means either the tumor was much smaller than 3 cc (about 1 cc would make the math work) or else the tumor was much higher grade that 3+4. I doubt the former since the size of 3 cc is pretty consistent with the percentage of biopsy core length that was positive. And I doubt the latter since the biopsy was graded at two different labs (3+3) the first time and (3+4) the second time, and then the path report showed 3+4.) So that's all pretty consistent. Or it's possible that the model simply has a lot of variation from one to the next and the discrepancy doesn't really mean much.

If you want to do your own math, see and look under the heading "prostate gland volume"

Any thoughts? Thanks in advance.

Veteran Member

Date Joined Mar 2010
Total Posts : 1152
   Posted 2/16/2011 7:22 AM (GMT -6)   
Hi proscapt,

I dont think your calculations are right.
3 ccs of 3+4 tumour shoud give you 2.92x3cc=8.8nl of psa + 2.5 nl from healthy tissue. This adds up to about 11.3nl. However this is still much higher than your actual reading.
I had the same issue with my husbands reading of 2.69 before the op. 2.5 was from healthy prostate tissue. Pathologist 1 said he had 0.2cc of cancerous tissue 3+4. This lines up with a pre op score of 2.5+0.2x2.92=3.1 which is close. Pathologist 2, a pathologist favoured by dr strum thought that the tumour was more like 0.7cc which would indicate a preop reading of close to 4.6.

I think that the reason these numbers don't tie up is thst pathologists over or under estimate tumour and prostate volumes and dr strums model is not perfect. Most people with healthy prostates have a reading below 1 for their psa my dad's is a steady 0.7 and he is aged 75. According to dr strums model his prostate should be tiny, but actually he had surgery a few years ago for bph and i remember it was not.

Hope this helps.
Husband's age: 52. Sydney Australia.
Family history: Mat. grandfather died of PC at 72. Mat. uncle died of PC at 60. He has hereditary PC.
PSA: Aug07 - 2.5|Feb08 - 1.7|Oct09 - 3.67 (free PSA 27%)|Feb10 - 4.03 (free PSA 31%) |Jun10 - 2.69. DRE normal.
Biopsy 28Apr10: negative for a diagnosis of PC however 3 focal ASAPs “atypical, suspicious but not diagnostic” for PC. Review of biopsy by experienced pathologist, 1/12 core: 10% 3+3 (left transitional), 1/12 core: ASAP (left apex)
Nerve sparing RP, 20Aug10 with Dr Stricker. Post-op path: 3+4 (ISUP 2005). Neg (margins, seminal vesicles, extraprostatic extension). Multifocal, with main involvement in the fibro-muscular zone. T2C.
Post RP PSA,
Lab 1: Sep10 – 0.02|Nov10 – 0.03|Dec10 – 0.03
Lab 2: Nov 10 - 0.01|Dec10 – 0.01

John T
Veteran Member

Date Joined Nov 2008
Total Posts : 4269
   Posted 2/16/2011 1:06 PM (GMT -6)   
Some doctors have been using .1 instead of .666 to measure benign prostate psa. I would imagine that just with anything else there are variations between individuals. Also transition zone tumors created a lot more psa for their volume than tumors in other locations.
It's just one peice of information among many that give you a better picture of your status.
65 years old, rising psa for 10 years from 4 to 40; 12 biopsies and MRIS all negative. Oct 2009 DXed with G6 <5%. Color Doppler biopsy found 2.5 cm G4+3. Combidex clear. Seeds and IMRT, no side affects and psa .1 at 1.5 years.

Regular Member

Date Joined Dec 2010
Total Posts : 144
   Posted 2/16/2011 4:26 PM (GMT -6)   
the math doesn't seem right - is it possible that gleason 3 leaks PSA at a greater rate than gleason 4 ? you have 3 time time the gleason 3 as gleason 4, but the gleason 3 seems to contribute 6 times as much PSA roughly. (9.6 vs 1.5)
Age at diagnosis 48
Gleason 3+3
Pre-Surgery PSA 5.1, 5.7
Cores Positive: 10 of 12 up to 40%
Treatment: open Surgery Dec 2010

Veteran Member

Date Joined Aug 2010
Total Posts : 644
   Posted 2/16/2011 9:07 PM (GMT -6)   

Thanks for your feedback, but I think the math is right. According to the Strum model, higher grades of PC leak much less PSA because so much genetic change has occurred that they no longer generate much PC.

G3 generates about 4.25 ng per cc of tumor volume.
G4 generates about 2 ng per cc of tumor.

2.25 cc of G3 + .75 cc of G4 should generate 9.6 and 1.5 ng of PSA respectively.

Regular Member

Date Joined Feb 2011
Total Posts : 173
   Posted 2/16/2011 9:26 PM (GMT -6)   
Who is strum? Thanks

Veteran Member

Date Joined Aug 2010
Total Posts : 644
   Posted 2/16/2011 9:34 PM (GMT -6)   
Trepidation - He's Stephen B. Strum, a very highly regarded oncologist specializing in PC, located in Ashland Oregon.

See the URL link in the first post in this thread for more.

Post Edited (proscapt) : 2/16/2011 8:11:02 PM (GMT-7)

Veteran Member

Date Joined Jul 2008
Total Posts : 966
   Posted 2/17/2011 1:22 PM (GMT -6)   

Just got back from the oncologist who is doing the clinical trial I am in. He said that the psa leak was 3.32 per cc for G6. I have no idea where he got his figures from, but thought I would pass that along. Punch in his numbers and see what you come up with. (BTW, my tumor volumn didn't calculate using the 3.32 either.) I had a 6 cc tumor and 50 cc gland but psa was 4.4.
You are beating back cancer, so hold your head up with dignity


Robotic Surgery Sept 2008
PSA increasing since January 2009
Current PSA .44 (29 months)
PSA Doubling time approx. 6 months
Clinical Trial - SRT begins 2/21/11

Veteran Member

Date Joined Aug 2010
Total Posts : 644
   Posted 2/17/2011 1:35 PM (GMT -6)   
Thanks, LV-TX... that gets closer to working out arithmetically.

My guess is there's probably pretty wide confidence interval (standard deviation) at work here. Maybe the point is that the leakage math is valuable in the pre-treatment context when it helps estimate the likelihood of EPE and SVI, or when it helps to raise suspicion about an apparently clean biopsy -- but maybe not so useful in a post-treatment setting, when the path report supersedes it.
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