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In Reply

Department of Radiation Oncology, BrighamWomen's HospitalDana Farber Cancer Institute, Boston, MA

Ming-Hui Chen

Department of Statistics; University of Connecticut, Storrs, CT

We wish to thank Dr Roach for his kind words and his careful reflection on our study.¹ We also agree that the conclusion of a pooled analysis of randomized studies not designed specifically to address a cardiovascular end point is hypothesis generating. We do, however, want to address the two specific concerns that Dr Roach raised about our study.

First, the cut point of age 65 years was selected for illustrative purposes because age as a continuous variable was shown to be significantly associated with time to a fatal myocardial infarction (MI) following randomization in both the analysis of the United States (US)/Australian and Canadian/Australian pooled cohorts in our study.¹ Age 65 years was selected, as described in our study, based on the hypothesis generating subgroup analysis of the watchful waiting (WW) versus radical prostatectomy (RP) randomized study.² That particular study suggested that RP as compared to WW performed in men with similar types of prostate cancer to the men in our study did not lead to a prolongation in survival if they were beyond age 65 years. Therefore, the use of age 65 years as a cut point is reasonable when considering an intervention that may cause a premature death. However, we could have selected age 70 years and our conclusion would have remained unchanged.

Second, the median follow-up of the Canadian study³ was nearly 2 years shorter than the US study (4.8 v 6.7 years, respectively). Therefore, when you combine the 6-month androgen suppression therapy arms of the US and Australian⁴ studies and compare these data to the combined data from the 8-month and 6-month arms of the Canadian and Australian studies, a follow-up bias can be introduced. This bias can lead to a lower cumulative incidence of fatal MIs in the Canadian/Australian as compared to the US/Australian pooled data set that simply reflects the shorter time over which to observe fatal MIs. This is what is demonstrated in the figure provided by Dr Roach in his letter. As a result of this follow-up bias, we created two separate figures.

We hope that this helps to clarify our methodology, and we would again like to thank Dr Roach for his thoughtful commentary.

AUTHORS' DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST

The author(s) indicated no potential conflicts of interest.

REFERENCES

1. D'Amico AV, Denham JW, Crook J, et al: Influence of androgen suppression therapy for prostate cancer on the frequency and timing of fatal myocardial infarctions. J Clin Oncol 25:2420-2425, 2007[Abstract/Free Full Text]

2. Bill-Axelson A, Holmberg L, Ruutu M, et al: Scandinavian Prostate Cancer Group Study No 4: Radical prostatectomy versus watchful waiting in early prostate cancer. N Engl J Med 352:1977-1984, 2005[Abstract/Free Full Text]

3. Crook J, Ludgate C, Malone S, et al: Report of a multi-center Canadian phase III randomized trial of 3 months vs 8 months neoadjuvant androgen deprivation before standard-dose radiotherapy for clinically localized prostate cancer. Int J Radiat Oncol Biol Phys 60:15-23, 2004[CrossRef][Medline]

4. Denham J, Steigler A, Lamb DS, et al: Short-term androgen deprivation and radiotherapy for locally advanced prostate cancer: Results from the Tran-Tasman Radiation Oncology Group 96.01 randomised controlled trial. Lancet Oncol 6:841-850, 2005[CrossRef][Medline]

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