A comparison of the single and double factor high-risk models for risk assignment of prostate cancer treated with 3D conformal radiotherapy

Two models for stratification of prostate cancer aggressiveness predominate for the purposes of daily treatment decision making. This study investigates the relationships between these two clinically popular models. Both risk stratification models use the same definition for low risk: Gleason score (GS) ≤6, pretreatment initial prostate specific antigen (iPSA) ≤10 ng/mL, and stage T1c–T2c. For the single factor high risk model (SF), intermediate risk (IR) is defined as the presence of GS 7 or PSA > 10–20 ng/mL, without the presence of any high-risk feature; high risk (HR) was defined as the presence of GS 8–10, iPSA >20, or palpation stage T3. For the double factor high risk (DF) model, IR and HR were defined as one and more than one of the following: GS ≥7, iPSA >10, or stage T3. Between April 1989 and October 2001, 1,597 patients were treated definitively with 3D conformal radiation therapy (3D-CRT) alone for prostate cancer at our institution. The main clinical endpoint was freedom from biochemical failure (FFBF). The 5-year actuarial FFBF rate for the low-risk group was 83%. The SF model resulted in FFBF rates of 76% and 47% for IR and HR patients respectively. The DF model resulted in FFBF rates of 70% and 52% for IR and HR patients, respectively. The FFBF rate for patients defined as IR and HR by both models was 76% and 40%, respectively. Those classified as IR by the DF model and then further subdivided into IR and HR by the SF model had a 76% and 52% 5-year FFBF rate ( p = 0.0004). Those classified as HR by the DF model and then further subdivided into IR and HR by the SF model had a 71% and 40% 5-year FFBF ( p = 0.0014). The SF model created prognostic groups with a greater internal consistency than the DF model. The SF was also better at identifying patients with high-risk prostate cancer who may benefit from a more aggressive approach.