PV QA 1 - Poster Viewing Q&A 1
Purpose/Objective(s): Previous studies have shown that anticoagulation or antiplatelet medication reduces the risk of recurrence in men with prostate cancer. We tested the hypothesis that platelet count would also be associated with outcome, as a possible mechanism for the favorable effect of these medicines on outcome.
Materials/Methods: 705 patients received radiotherapy (RT) for non-metastatic prostate cancer between 1989-2006. Median age was 69 y, median PSA was 8.4. NCCN risk was low/intermediate/high risk in 37/37/26%, respectively. 41% received androgen deprivation therapy (ADT), for a median 4 mo. The median dose of RT was 72 Gy, and 15% of patients were treated with brachytherapy. Medicines including anticoagulant (AC, e.g. warfarin, clopidogrel) or antiplatelet therapy (asa) were documented at consultation or follow-up. 199 men took AC (n=82) or aspirin (n=142). 596 men had platelet counts available; >90% were extracted within 6 mo of RT. The effect of AC/asa use and platelet counts were analyzed with respect to freedom from biochemical failure (FFBF, nadir+2), distant metastasis (FFDM), and cause specific survival (CSS) on univariate (UVA) and multivariate analysis (MVA).
Results: After a median follow-up of 99 mo, FFBF-5y was 82%. At 10-y, FFBF, FFDM, and CSS were 66%, 91%, and 94%, respectively. On univariate analysis, men treated with AC/asa had improved FFBF, FFDM, and CSS (all p<0.05). On logistic regression, platelet count was associated with recurrence (p=0.04). Stratified by median value (218), platelets were not associated with disease control, however the lowest quartile (<183) was associated with lower FFBF (p<0.01) and FFDM (p=0.02), but not CSS (p=0.16). On MVA for FFBF, risk category, platelet<183, and AC/asa use were associated with outcome (p<0.05) while ADT was not (p=0.79). On MVA for FFBF, risk category (p<0.01), platelet <183 (RR 2.0, p<0.01), and AC/asa use (RR 0.64, p=0.02) were associated with outcome while ADT was not (p=0.61), in distinction from a separate MVA for FFBF including only risk category (p<0.01) and ADT (p=0.05) showing both factors to be associated with outcome. On MVA for FFDM, risk category (p<0.01), platelet<183 (RR 2.1, p=0.03), and AC/asa use (RR 0.45, p=0.03) were associated with outcome while ADT (p=0.78) was not. The potential for interaction between AC/asa or ADT use and platelet<183 was further explored testing subsets on UVA for FFDM. Notably, the favorable effects of both AC/asa use and ADT were limited to men with plt>183. Similarly, the adverse association of plt<183 was more strongly appreciated in men receiving no AC/asa (FFDM-10y 83% vs 92%, p=0.04) or no ADT (88% vs 97%, p<0.01), whereas plt<183 was not negatively associated with FFDM in men on AC or ADT.
Conclusion: Lower platelet count is associated with a 2-fold increased rate of DM after prostate radiation therapy. Low platelet count may serve as a surrogate for tumor-platelet interactions that influence disease recurrence, which may be modified by AC/asa or hormonal therapy.
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