title: Determining if pretreatment PSA doubling time predicts PSA trajectories after radiation therapy for localized prostate cancer.
abstract: BACKGROUND
  To determine if pretreatment PSA doubling time (PSA-DT) can predict post-radiation therapy (RT) PSA trajectories for localized prostate cancer.
  
  
  METHODS
  Three hundred and seventy-five prostate cancer patients treated with external beam RT without androgen deprivation therapy (ADT) were identified with an adequate number of PSA values. We utilized a linear mixed model (LMM) analysis to model longitudinal PSA data sets after definitive treatment. Post-treatment PSA trajectories were allowed to depend on the pre-RT PSA-DT, pre-RT PSA (iPSA), Gleason score (GS), and T-stage.
  
  
  RESULTS
  Pre-RT PSA-DT had a borderline impact on predicting the rate of PSA rise after nadir (p=0.08). For a typical low risk patient (T1, GS6, iPSA 10), the predicted PSA-DT post-nadir was 21% shorter for pre-RT PSA-DT<24month compared to pre-RT PSA-DT>24month (19month vs. 24month). Additional significant predictors of post-RT PSA rate of rise included GS (p<0.0001), iPSA (p<0.0001), and T-stage (p=0.02).
  
  
  CONCLUSIONS
  We observed a trend between rapidly rising pre-RT PSA and the post-RT post-nadir PSA rise. This effect appeared to be independent of iPSA, GS, or T-stage. The results presented suggest that pretreatment PSA-DT may help predict post-RT PSA trajectories.
authors.affiliation: Department of Radiation Oncology, University of Michigan, USA. dsoto@med.umich.edu
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Soto
authors.forename: Rebecca R
authors.initials: RR
authors.lastname: Andridge
authors.forename: Charlie C
authors.initials: CC
authors.lastname: Pan
authors.forename: Scott G
authors.initials: SG
authors.lastname: Williams
authors.forename: Jeremy M G
authors.initials: JM
authors.lastname: Taylor
authors.forename: Howard M
authors.initials: HM
authors.lastname: Sandler
mesh_terms: D000368:Aged; D006801:Humans; D008297:Male; D009367:Neoplasm Staging; D017430:Prostate-Specific Antigen / Q000097:blood*; D011471:Prostatic Neoplasms / Q000097:blood* / Q000473:pathology / Q000532:radiotherapy*
chemical_list: D017430:Prostate-Specific Antigen