ORLANDO—Maximal tumor diameter (MTD) may predict which prostate cancer patients are at very low risk of PSA failure following radical prostatectomy who may not benefit from adjuvant radiation therapy, according to study findings presented at the American Urological Association 2014 annual meeting.

MTD identified patients at low risk of PSA failure even in the presence of adverse features such as a high Gleason score of extracapsular extension, which are associated with a high risk of PSA failure, according to investigator Brent S. Rose, MD, a radiation oncology resident in the Harvard Radiation Oncology Program in Boston.

“People with a really small tumor who had these adverse risk features still did really well, whereas if you had a big tumor and these high risk features, then you did poorly, as might be expected,” Dr. Rose said.

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Dr. Rose and colleagues studied 354 men with T1c-T2 PCa who underwent radical prostatectomy without adjuvant therapy. The MTD was defined as the maximal linear dimension of the largest single focus of tumor. After a median follow-up of 4.0 years, 34 men (9.6%) experienced PSA relapse. On multivariable analysis, increasing MTD, PSA, pathologic Gleason score, T stage, and positive surgical margins were significantly associated with an increased PSA failure risk. Among men with a pre-RP PSA level above 4 ng/mL—but not in those with a PSA of 4 ng/mL or less—the 5-year estimated PSA failure-free survival rate was significantly lower in patients whose MTD was larger than 1.2 cm (the median MTD for the entire cohort) compared with those with an MTD of 1.2 cm or smaller (74.5% vs. 99.0%). If a patient had at least 1 adverse feature, such as pT3 disease or a Gleason score of 8 or higher, the 5-year estimated PSA failure-free survival rates were 46.6% and 100% for men whose MTD was larger than 1.2 cm and 1.2 cm or smaller, respectively.