Prostate weight and risk for positive margins at surgery

A new study has clearly shown that men with lighter (and therefore smaller) prostates are at greater risk for positive surgical margins after robot-assisted laparoscopic prostatectomy (RALP) than men with heavier (and therefore larger) prostates.

Marchetti et al. carried out a retrospective analysis of data from 690 men with low-risk prostate cancer (clinical stage T1c, PSA < 10 ng/ml, biopsy Gleason score ≤ 6) who were treated by RALP with bilateral nerve-sparing at the University of Chicago by one or other of two surgeons between 2003 to 2009. Data on prostate weight (PW) was obtained from the pathologic specimen.

The results of this analysis are as follows:

  • 105/690 patients (15.2 percent) had a positive surgical margin (PSM).
  • Patients with PSMs had higher PSA levels, smaller prostates, higher Gleason scores, and higher pathologic stages than men with no PSMs.
  • There was a significant inverse relationship between PSM and PW after adjustments for the surgeon’s experience and the patient’s age, body mass index, pathologic Gleason score, and pathologic stage.
  • The predicted probabilities of PSMs for prostates weighing 25, 50, 100, and 150 g  were 22, 13, 5, and 1 percent, respectively.

If PW is independently associated with a higher probability of PSM in low-risk patients who have a bilateral nerve-sparing RALP, then this is almost certainly true for prostate volume too, because prostate tissue density doesn’t vary significantly for man to man.

It make perfect sense that men with smaller prostates are at greater risk for positive surgical margins than men with larger prostates. The surgeon is having to work in a more confined space to remove a smaller organ. This significantly increases the importance of the skill of the surgeon to avoid risk for positive surgical margins while still sparing the nerves.

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