PSA Doubling Time
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PSADT has been evaluated in patients with a rising PSA after local treatment with either RP or RT.1 In these settings, PSADT has been significantly shorter in patients who developed metastases, than in those who did not develop metastatic disease. For example, the mean PSADT in the RP and RT groups who developed metastatic disease was approximately five months and six months, respectively. These PSADTs and the PSADTs for other groups are shown below.

PSA Doubling Times in Months after RP and RT: Median values

Treatment

PSADT (range)

PSA elevation only Local recurrence Metastatic disease
RP 19 (2.1-90) 39 (4.1-300) 4.7 (0.8-7.9)
RT 21 (5-63.8) 14 (4.5-42.9) 6.2 (3.7-10.7)

There was no statistically significant difference between RP and RT except for local recurrence. In the local recurrence category, the RP value may have been unduly lengthened by the single case with the longest doubling time (300 months). Within the RP and the RT groups, there was a decrease in PSADT with increasing tumor grade. Therefore, the use of PSADT is of significant value in the treatment planning of patients with a rising PSA post-RP or post-RT.

If the PSADT is < 10 months, there is a high probability of metastatic disease. Patients post-RP with a short PSADT are therefore not good candidates for local RT employed in an attempt to cure the patient. A bone scan and/or ProstaScint scan in this setting may be used to confirm metastatic disease. Patients with a long PSADT would be potential candidates for RT after RP, providing that their Partin II analysis, using the findings at RP (Gleason score and status of seminal vesicles and lymph nodes), along with the PSA velocity after RP, did not indicate a high probability of systemic recurrence. Again, in such patients, a bone scan and/or ProstaScint scan should show no evidence of activity outside the prostate area. Similarly, patients with a rising PSA and a short PSADT after RT have a high likelihood of metastatic disease. In contrast, patients with a long PSADT after RT might be candidates for salvage cryosurgery.

In a study by Fowler et al, (1995) the median PSADT in patients with localized PC without metastases was 7.5 months contrasted with 2.5 months in patients with localized PC and new metastases.2 This seems to imply that in patients newly diagnosed with PC, the evaluation of PSADT may have value in determining risk for non-organ-confined disease. This implication needs to be explored in prospective studies; it has been true in the patients we have seen.

PSADT should be based on at least three values separated by at least three months each. PSADT is best calculated with a mathematical log-slope method. You will find a good PSA Doubling time calculator and several other nomograms available from Memorial Sloan Kettering at: 
http://nomograms.mskcc.org/Prostate/PsaDoublingTime.aspx

For more information on Algorithms/Nomograms and Software

 

References:

  1. Fowler JE, Pandey P, Braswell NT, et al: Prostate specific antigen progression rates after radical prostatectomy or radiation therapy for localized prostate cancer. Surgery 116: 302-306, 1994.
  2. Fowler JE, Pandey P, Seaver LE, et al: Prostate specific antigen regression and progression after androgen deprivation for localized and metastatic prostate cancer. J Urol 153:1860-1865, 1995.