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BACKGROUND: Prostate size is associated with a number of negative prognostic indicators. We evaluated the effect of prostate size on biochemical recurrence following radical prostatectomy.
METHODS: We conducted a retrospective review of patients with Gleason 6-10 prostate cancer who underwent radical retropubic prostatectomy at the Massachusetts General Hospital from 1993 - 1999. Patients were excluded if they received neoadjuvant therapy, had less than 8 weeks of follow-up, or PSA did not fall below 0.2 ng/ml post-operatively. Biochemical recurrence was defined as a PSA rise to 0.2 ng/ml or greater with a confirmatory value if available. Cox proportional hazards models were used to evaluate for association between variables and biochemical recurrence.
RESULTS: A total of 877 patients underwent surgery with a mean follow-up of 7.5 ± 4.5 years (range 0.2 - 16.3). Mean age, PSA, and prostate weight were 61.0 ± 6.9 years, 7.3 ± 5.5 ng/ml, and 46.7 ± 19.1 grams, respectively. Gleason score was distributed as follows: 6 in 422 patients (48.1%), 7 in 372 patients (42.4%), and 8-10 in 83 patients (9.5%). Using univariate Cox proportional hazards models, older age, higher PSA, higher Gleason score, presence of pT3 or pT4 disease, positive margins, and smaller prostate weight were associated with biochemical recurrence (p < 0.05 for each). After stepwise addition of each variable in a multivariate Cox model, prostate weight lost significance only when Gleason score was included in the model. To assess for effect modification, multivariate Cox models were stratified by Gleason score (Table 1). In this analysis, prostate weight was associated with biochemical recurrence only for Gleason 7 disease, but margin status was associated with recurrence for Gleason 6 disease.
CONCLUSIONS: Smaller prostate size is independently associated with biochemical recurrence for Gleason 7 disease while a positive surgical margin is associated with biochemical recurrence for Gleason 6 disease. These results have implications in the management of patients with small prostate glands.

Table 1: Multivariate Cox proportional hazards model stratified by Gleason score

	HR Gleason 6	p-value Gleason 6	HR Gleason 7	p-value Gleason 7	HR Gleason 8-10	p-value Gleason 8-10
Age (years)	1.01	0.657	1.02	0.091	0.993	0.778
PSA (ng/mL)	1.04	0.312	1.05	<0.001	1.02	0.485
Prostate weight (grams)	0.985	0.147	0.986	0.023	1.01	0.355
pT3+ vs pT2	0.675	0.410	1.42	0.076	1.39	0.302
Positive Margin	3.98	<0.001	1.43	0.054	0.779	0.406