Brachytherapy May Reduce Treatment Failure in Obese Prostate Cancer Patients

by Charles Bankhead | MedPage Today | 08.21.2008

BOSTON, Aug. 21 -- Brachytherapy for prostate cancer appears to overcome the adverse effects of obesity that lead to high PSA failure rates with surgery and external beam radiation, investigators here have concluded.

In fact, PSA failure after brachytherapy had an inverse relationship with body mass index, Jason A. Efstathiou, M.D., Ph.D., of Massachusetts General Hospital, and colleagues, reported in the August issue of the International Journal of Radiation Oncology, Biology, and Physics.

PSA failure occurred in more than 30% of patients with a BMI <25, double the rate among patients with a BMI >30.

"The possibility that brachytherapy is a preferred treatment strategy for obese patients warrants further study," the authors concluded.

Greater BMI has been associated with an increased risk of PSA failure after radical prostatectomy and radiation therapy. Little is known, however, about PSA failure after brachytherapy, the authors said.

The issue warrants investigation because of the increasing use of brachytherapy, they continued. From 1994 to 1999, the number of prostate cancer patients treated with the technique increased 12-fold.

To examine the influence of obesity on PSA failure after brachytherapy, the investigators retrospectively analyzed medical records for 374 patients who had brachytherapy for nonmetastatic T1c-T2c prostate cancer.

In 13% of cases, patients received supplemental external-beam radiation therapy, and 35% received androgen deprivation therapy in addition to brachytherapy.

Height and weight data were available for 353 (94%) of the patients. Median age was 66, median baseline PSA was 5.7 ng/mL, and median BMI was 27.1. PSA failure was defined as PSA nadir level plus 2 ng/mL.

The analysis revealed 76 PSA recurrences during a median follow-up of six years.

The six-year failure rate by baseline BMI was:

• 30.2% for a BMI <25
• 19.5% for a BMI of 25 to 30
• 14.4% for a BMI ≥30 (P=0.19 for trend)

The results remained unchanged in analyses that considered BMI as a continuous variable, that used different definitions of PSA failure, and that excluded patients who had supplemental external beam radiation or androgen deprivation therapy.

In a multivariate analysis, only baseline PSA value predicted the time to PSA failure (P=0.0006).

The authors offered several potential explanations for BMI's apparent lack of influence on PSA failure after brachytherapy:

• Brachytherapy is reserved for low-risk patients who already have a reduced risk of PSA failure.
• Obesity tends to reduce testosterone values and increase estradiol levels, which may lead to underdetection of biochemical failure.
• The definition of biochemical failure remains controversial.

The researchers did note several limitations of the study, including the retrospective design, which is subject to selection biases.

They also noted that they lacked complete information about patients' lifestyle and comorbidities, which may have mediated the effect of obesity. Nor did they have postimplantation dosimetric data for a number of patients.

Finally, they acknowledged, "some types of indolent PSA failure may be an inaccurate surrogate end point for cancer-specific mortality."

The authors reported no potential conflicts of interest.

Primary source: International Journal of Radiation Oncology, Biology, and Physics
Source reference:
Efstathiou J et al. "Body mass index and prostate-specific antigen failure following brachytherapy for localized prostate cancer" Int J Radiation Oncol Biol Physics 2008; 71: 1302-1308.

Copyright MedPage Today 2008