AUA 2018: Risk of Secondary Bladder Cancer After High Dose Rate Brachytherapy for Prostate Cancer

San Francisco, CA (UroToday.com) Treatment-induced secondary cancers are well described following radiotherapy for prostate cancer. While the majority of the literature has focused on external beam radiotherapy, the risk associated with brachytherapy appears to be somewhat less. To date, only the association between low dose rate brachytherapy and secondary cancers has been examined. However, high dose rate brachytherapy is increasingly being utilized. In a moderated poster at the American Urologic Association Annual Meeting, Dr Miyaji and colleagues from Kurashiki, Japan described their single center experience with secondary bladder cancers following high dose rate brachytherapy (HDR-BT), with or without external beam radiotherapy (EBRT).

The authors present a matched case-control study of patients who developed bladder cancer following treatment of localized prostate cancer. They first identified 1023 patients who underwent HDR-BT between 1998 and 2014. Of these, 83 patients received HDR-BT alone and the remainder received concomitant EBRT. Prior to July 2006, patients received 24 Gy/4 fractions of HDR-BT with 36.9 Gy of EBRT to the prostate. Subsequently, the treatment regime was changed to 18-20 Gy/2 fractions with 39 Gy of EBRT. Over the same period, 285 patients at their institution underwent radical prostatectomy.

The authors designed their case-controlled analysis to include only metachronous tumors, which could feasibly be treatment-induced. Therefore, they excluded cases where bladder cancer was diagnosed within 2 years of the prostate cancer treatment and patients with a history of urothelial carcinoma prior to prostate cancer treatment.

They identified 16 patients newly diagnosed with bladder cancer. All patients were found to have microscopic hematuria and underwent TURBT which confirmed non-muscle invasive disease.

Using a 1:8 match based on age at the time of prostate cancer treatment and duration of follow-up, 128 controls were identified. Logistic regression analyses examined the association between prostate cancer treatment modality and the development of bladder cancer while accounting for smoking history.

Of the 16 patients diagnosed with bladder cancer, 1 underwent RP and 15 underwent HDR-BT (13 HDR-BT with EBRT and 2 HDR-BT alone). In the control group, 36 (28%) patients underwent RP and 92 (72%) underwent HDR-BT +/- EBRT. On logistic regression analysis, HDR-BT, as compared to radical prostatectomy, was associated with a significantly increased likelihood of bladder cancer diagnosis (OR 5.38, 95% CI 1.02-99.32, p=0.047). Time to diagnosis of bladder cancer was 56 months (24-160 months) since prostate cancer treatment.

The authors conclude that HDR-BT may increase the incidence of bladder cancer and should be included in the informed consent process for patients considering HDR-BT.

Presented By: Yoshiyuki Miyaji
Co-authors: Tota Nakatsuk, Hiroyasu Takasaki, Seitetsu Kin, Shin Ohira, Masaichiro Fujita, Shinjiro Shimizu, Shohei Tsukimori, Mikako Kaifu, Ryoei Hara, Tomohiro Fujii, Atsushi Nagai

Written by: Christopher J.D. Wallis, Urology Resident, University of Toronto, Twitter: @WallisCJDat the 2018 AUA Annual Meeting - May 18 - 21, 2018 – San Francisco, CA USA

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