2 abstracts

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Thursday, 29 November 2007

MacCallum Cancer Centre and University of Melbourne, Melbourne,

Australia

To define and incorporate the impact of the percentage of positive biopsy

cores (PPC) into a predictive model of prostate cancer radiotherapy

biochemical outcome

The data of 3264 men with clinically localized prostate cancer treated with

external beam radiotherapy at four institutions were retrospectively

analyzed. Standard prognostic and treatment factors plus the number of

biopsy cores collected and the number positive for malignancy by transrectal

ultrasound-guided biopsy were available. The primary endpoint was

biochemical failure (bF, Phoenix definition). Multivariate proportional

hazards analyses were performed and expressed as a nomogram and the model's

predictive ability assessed using the concordance index (c-index).

The cohort consisted of 21% low-, 51% intermediate-, and 28% high-risk

cancer patients, and 30% had androgen deprivation with radiotherapy. The

median PPC was 50% (interquartile range [iQR] 29-67%), and median follow-up

was 51 months (IQR 29-71 months). Percentage of positive biopsy cores

displayed an independent association with the risk of bF (p = 0.01), as did

age, prostate-specific antigen value, Gleason score, clinical stage,

androgen deprivation duration, and radiotherapy dose (p < 0.001 for all).

Including PPC increased the c-index from 0.72 to 0.73 in the overall model.

The influence of PPC varied significantly with radiotherapy dose and

clinical stage (p = 0.02 for both interactions), with doses <66 Gy and

palpable tumors showing the strongest relationship between PPC and bF.

Intermediate-risk patients were poorly discriminated regardless of PPC

inclusion (c-index 0.65 for both models).

Outcome models incorporating PPC show only minor additional ability to

predict biochemical failure beyond those containing standard prognostic

factors.

Written by

SG, Buyyounouski MK, Pickles T, Kestin L, ez A, Hanlon AL,

Duchesne GM.

Reference

Int J Radiat Oncol Biol Phys. 2007 Oct 27; [Epub ahead of print]

doi:10.1016/j.ijrobp.2007.08.021

PubMed Abstract

PMID:17967518

Thursday, 29 November 2007

Department of Radiation Oncology, Fox Chase Cancer Center, Philadelphia,

Pennsylvania

The American Society for Therapeutic Radiology and Oncology (ASTRO)

definition of biochemical failure (BF) incorporates backdating, resulting in

an artificial flattening of Kaplan-Meier curves and overly favorable

estimates when follow-up is short. The nadir + 2 ng/mL (Nadir + 2; Phoenix)

definition reduces these artifacts. The objective of the current study was

to compare ASTRO and Phoenix BF estimates as determinants of distant

metastasis (DM), cause-specific mortality (CSM), and overall mortality (OM).

A total of 1831 patients with T1-4N0M0 prostate cancer were treated with

external beam radiotherapy (RT) using conventional or three-dimensional

conformal methods to at least 60 grays (Gy). The median follow-up was 71

months and the median RT dose was 72 Gy (range, 60-79 Gy). regression

models incorporating BF as a time-dependent covariate were used for both

univariate and multivariate analyses. Other covariates included in the

analyses were T classification, Gleason score, neoadjuvant/adjuvant androgen

deprivation, age, RT dose, and pretreatment prostate-specific antigen.

BF was observed in 389 men (21%) using the Phoenix definition and 460 men

(25%) using the ASTRO definition. DM was observed in 84 patients (5%), 48

patients (3%) patients died of prostate cancer, and 404 patients (22%) died

of any cause. The Phoenix definition of BF was found to be a significant

predictor of DM, CSM, and OM, after controlling for other significant

covariates. The ASTRO definition was found to be associated with CSM and DM,

but not OM.

The Phoenix definition of BF is a more robust determinant of patient outcome

compared with the ASTRO definition. The correlation with mortality,

including OM, and the independence of this correlation from the use of

neoadjuvant/adjuvant androgen deprivation, supports the use of Nadir + 2 in

prostate cancer clinical trials of RT with or without androgen deprivation.

Cancer 2007. © 2007 American Cancer Society.

Written by

Abramowitz MC, Li T, Buyyounouski MK, Ross E, Uzzo RG, Pollack A, Horwitz

EM.

Reference

Cancer. 2007 Oct 29; [Epub ahead of print]

doi:10.1002/cncr.23139

PubMed Abstract

PMID:17968996

C. Meade

 

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