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Abstract
Purpose: This study proposed the optimal definition of biochemical recurrence (BCR) after salvage radiotherapy (SRT) following radical prostatectomy for prostate cancer.

Materials and methods: Among 1,117 patients who had received SRT, data from 205 hormone-naïve patients who experienced post-SRT prostate-specific antigen (PSA) elevation were included in a multi-institutional database. The primary endpoint was to determine the PSA parameters predictive of distant metastasis (DM). Absolute serum PSA levels and the prostate-specific antigen doubling time (PSA-DT) were adopted as PSA parameters.

Results: When BCR was defined based on serum PSA levels ranging from 0.4 ng/mL to nadir+2.0 ng/mL, the 5-year probability of DM was 27.6%-33.7%. The difference in the 5-year probability of DM became significant when BCR was defined as a serum PSA level of 0.8 ng/ml or higher (1.0-2.0 ng/mL). Application of a serum PSA level of ≥ 0.8 ng/mL yielded a c-index value of 0.589. When BCR was defined based on the PSA-DT, the 5-year probability was 22.7%-39.4%. The difference was significant when BCR was defined as a PSA-DT ≤ 3 months and ≤ 6 months. Application of a PSA-DT ≤ 6 months yielded the highest c-index (0.660). These two parameters complemented each other; for patients meeting both PSA parameters, the probability of DM was 39.5%-44.5%; for those not meeting either parameter, the probability was 0.0%-3.1%.

Conclusion: A serum PSA level > 0.8 ng/mL was a reasonable threshold for the definition of BCR after SRT. In addition, a PSA-DT ≤ 6 months was significantly predictive of subsequent DM, and combined application of both parameters enhanced predictability.

Affiliations

Sung Uk Lee 1, Jae-Sung Kim 2, Young Seok Kim 3, Jaeho Cho 4, Seo Hee Choi 5, Taek-Keun Nam 6, Song Mi Jeong 7, Youngkyong Kim 8, Youngmin Choi 9, Dong Eun Lee 10, Won Park 11, Kwan Ho Cho 1
1The Proton Therapy Center, Research Institute and Hospital, National Cancer Center, Goyang, Korea.
2Department of Radiation Oncology, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea.
3Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
4Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea.
5Department of Radiation Oncology, Yongin Severance Hospital, Yonsei University College of Medicine, Yongin, Korea.
6Department of Radiation Oncology, Chonnam National University Hwasun Hospital, Chonnam National University College of Medicine, Hwasun, Korea.
7Department of Radiation Oncology, Ewha Womans University Medical Center, Ewha Womans University College of Medicine, Seoul, Korea.
8Department of Radiation Oncology, Kyung Hee University Hospital, Kyung Hee University College of Medicine, Seoul, Korea.
9Department of Radiation Oncology, Dong-A University Hospital, Dong-A University School of Medicine, Busan, Korea.
10Biostatistics Collaboration Team, Research Institute and Hospital, National Cancer Center, Goyang, Korea.
11Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.