The PSA nadir that indicates potential cure after radiotherapy for prostate cancer

The prostate-specific antigen nadir that indicates potential cure by radiotherapy has never been established. We determined this nadir level and used it to define precisely disease freedom after radiotherapy.

Combination radioactive 125I prostate implant followed by external-beam radiation was administered to 660 men with clinical Stage T1T2N0 prostate cancer. The average pretreatment prostate-specific antigen level (Tandem R Assay) was 11.7 ng/mL (median 8.0 ng/mL, range 0.3 to 188 ng/mL). To analyze these data, recurrence was defined as a prostate-specific antigen level rising above whatever nadir was achieved. The median follow-up is 42 months (range 12 to 150 months).

Eighty-one percent of all men are calculated to achieve a prostate-specific antigen nadir of 0.5 ng/mL or less and to have a 5- and 10-year disease-free survival rate of 93% and 83%, respectively, as compared with a 5-year disease-free survival rate of 26% for those achieving a nadir of 0.6 to 1.0 ng/mL--a significant difference (P = 0.0001). All men with a nadir greater than 1.0 ng/mL ultimately failed treatment. Of 201 men with a minimum 5-year follow-up, 143 are disease-free and 140 (98%) achieved and maintained a nadir of 0.5 ng/mL or less.

For possible cure of prostate cancer with radiotherapy, a prostate-specific antigen nadir of 0.5 ng/mL or less should be achieved. With this nadir level, disease freedom after irradiation is defined as achievement and maintenance of a nadir of 0.5 ng/mL or less. A nadir greater than 0.5 ng/mL or subsequent increase above 0.5 ng/mL is defined as irradiation treatment failure. This definition may help resolve the controversy about the potential for cure of prostate cancer by irradiation.