Very high-risk locally advanced prostate ductal adenocarcinoma cured using low-dose-rate brachytherapy, with seminal vesicle implantation in combination with external beam radiotherapy at a biologically effective dose ≥ 220 Gy: two case reports with a long-term follow-up

PURPOSE: Prostate ductal adenocarcinoma (PDA) is an aggressive, rare variant of histologic sub-type of prostate cancer. Patients with PDA present with more aggressive clinical features and have a poorer prognosis than patients with acinar adenocarcinoma. So far, an optimal treatment for PDA has yet to be established. Furthermore, the effectiveness of low-dose-rate (LDR) brachytherapy for PDA has not been reported previously. CASE PRESENTATION: In this paper, we present two case reports on very high-risk locally advanced PDA, in which patients were successfully treated with LDR brachytherapy, with seminal vesicle implantation in combination with external beam radiotherapy (EBRT) at a biologically effective dose (BED) ≥ 220 Gy and short-term androgen deprivation therapy (ADT). There was no grade 2 genitourinary (GU) and gastrointestinal (GI) toxicities during follow-up, and no evidence of hematuria nor rectal bleeding during follow-up. The patients stay healthy without biochemical failure and without bowel or urinary difficulties at 11.5 years and 8 years, respectively. CONCLUSIONS: High-BED LDR-based radiotherapy in combination with EBRT (BED ≥ 220 Gy) may be an ideal treatment for very high-risk locally advanced PDA patients.