MRI helps forecast prostate cancer prognosis

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MRI findings in patients who are scheduled to undergo radiation therapy for prostate cancer can help predict the likelihood that the cancer will return and spread post-treatment, according to a new study published in the April issue of Radiology.

"This is the first study to show that MRI detection and measurement of the spread of prostate cancer outside the capsule of the prostate is an important factor in determining outcome for men scheduled to undergo radiation therapy," said Fergus V. Coakley, MD, professor of radiology and urology, vice chair for clinical services and section chief of abdominal imaging in the department of radiology at University of California, San Francisco, and study co-author.

Coakley and colleagues sought to determine if MRI findings prior to radiation therapy were an indicator of possible recurrence and spread.

For the study, 80 men with biopsy-proved prostate cancer (mean age, 59 years) who underwent endorectal MR imaging of the prostate prior to external-beam radiation therapy were retrospectively identified and details of baseline tumor characteristics, treatment and outcome were recorded.

According to Coakley, two experienced readers independently reviewed all MRI studies and recorded tumor T stage and the radial diameter of extracapsular extension (if present). Univariate and multivariate stepwise Cox regression analyses were used to investigate the relationship between baseline imaging and clinical predictive variables and the end point of metastatic failure.

The results showed that at MR imaging, readers one and two, respectively, considered 50 and 60 patients to have T1 or T2 disease (organ-confined disease) and 30 and 20 patients to have T3 disease.

After a mean follow-up of 43 months, four patients developed metastases. Univariate Cox analysis revealed that baseline serum prostate-specific antigen level, presence of extracapsular extension at MR imaging, and degree of extracapsular extension were all significantly related to the development of metastases. Multivariate Cox analysis revealed that the sole independent predictive variable was mean diameter of extracapsular extension. In particular, three of five patients with extracapsular extension of more than 5 mm at pretreatment MR imaging developed metastases 24, 43 and 63 months after therapy.

Coakley and his colleagues concluded that the presence and degree of extracapsular extension at MR imaging prior to external-beam radiation therapy are important predictors of post treatment metastatic recurrence.

"Patients with substantial extracapsular spread of prostate cancer may wish to discuss options for more aggressive therapy with their treating physicians," Coakley said.