Abstract
PurposeTo assess whether the cellular proliferation marker Ki67 provides prognostic information and predicts response to radiation therapy fractionation in patients with localized prostate tumors participating in a randomized trial of 3 radiation therapy fractionation schedules (74 Gy/37 fractions vs 60 Gy/20 fractions vs 57 Gy/19 fractions).Methods and MaterialsA matched case–control study design was used; patients with biochemical/clinical failure >2 years after radiation therapy (BCR) were matched 1:1 to patients without recurrence using established prognostic factors (Gleason score, prostate-specific antigen, tumor stage) and fractionation schedule. Immunohistochemistry was used to stain diagnostic biopsy specimens for Ki67, which were scored using the unweighted global method. Conditional logistic regression models estimated the prognostic value of mean and maximum Ki67 scores on BCR risk. Biomarker–fractionation interaction terms determined whether Ki67 was predictive of BCR by fractionation.ResultsUsing 173 matched pairs, the median for mean and maximum Ki67 scores were 6.6% (interquartile range, 3.9%-9.8%) and 11.0% (interquartile range, 7.0%-15.0%) respectively. Both scores were significant predictors of BCR in models adjusted for established prognostic factors. Conditioning on matching variables and age, the odds of BCR were estimated to increase by 9% per 1% increase in mean Ki67 score (odds ratio 1.09; 95% confidence interval 1.04-1.15, P = .001). Interaction terms between Ki67 and fractionation schedules were not statistically significant.ConclusionsDiagnostic Ki67 did not predict BCR according to fractionation schedule in CHHiP; however, it was a strong independent prognostic factor for BCR.
Highlights
Prostate cancer (PCa) is the second most common cancer worldwide for males; more than 1.11 million new cases were diagnosed in 2012 [1]
The CHHiP trial was funded by Cancer Research UK (CRUK/06/16, C8262/A7253, C1491/A9895, C1491/ A15955, SP2312/021), the Department of Health and the National Institute for Health Research Cancer Research Network
Additional support for activities at the central receiving laboratory was provided by Prostate Cancer UK and the Movember
Summary
Prostate cancer (PCa) is the second most common cancer worldwide for males; more than 1.11 million new cases were diagnosed in 2012 [1]. In the developed world, increased prostate-specific antigen (PSA) testing means that most patients are diagnosed with localized disease, for which external beam radiation therapy (EBRT), brachytherapy, and prostatectomy are important radical treatment options. Recurrence rates after EBRT for localized PCa vary considerably, from approximately 10% to 40-50% [2, 3]. EBRT is delivered using a uniform fractionation schedule for all localized PCa (ie, a “one size fits all approach”). This is despite a wide variation in the biology of localized PCa [4], including proliferation rate [5]. Biomarkers predicting sensitivity to radiation therapy fraction size have recently been identified as a key area for radiobiological research [6]
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