Timing of docetaxel chemotherapy and impact on outcomes in metastatic castrate-resistant prostate cancer (MCRPC).

298 Background: Docetaxel use has led to a significant prolongation in overall survival (OS) in metastatic prostate cancer after castrate resistance, with a more substantial OS gain when used in combination with initial androgen deprivation therapy (ADT). There is however limited information on outcomes in patients who initially do not receive chemotherapy, perhaps through patient choice or impaired performance status, who become suitable for docetaxel, comparing earlier with later docetaxel treatment. Methods: We retrospectively reviewed patients’ electronic clinical and prescribing records diagnosed with MCRPC and treated with docetaxel from 01/01/2006 to 24/11/2016 in a single centre in the UK. Data was reviewed for number of individual treatments received pre and post chemotherapy, including initial ADT, enzalutamide, abiraterone, docetaxel, cabazitaxel, mitoxantrone, radium 223, single agent steroids and diethylstilboestrol. Prostate specific antigen (PSA) response, number of cycles and dosing of docetaxel and OS were also reviewed. Results: 168 consecutive patients with MCRPC receiving docetaxel were reviewed. Median Gleason grade across the three groups was 8. 48 patients (29%) received docetaxel after 1 or 2 previous treatments, 105 (63%) after 3 or 4 previous treatments and 15 (9%) after 5 or 6. PSA response rates were superior in the earlier treated group (61%, p=0.003), compared with 30% and 31% respectively in the later groups. Median number of cycles was 5.5 overall, with a mean weighted dose received of 396mg/m2, 373mg/m2 and 301mg/m2 in the after 1 or 2 treatments, after 3 or 4 treatments and after 5 or 6 treatment groups. Median OS from castrate resistance for the earlier group was 29 months, not significantly less (p=0.1) than the 35 months for an intermediate number of prior treatments and 42 months for the later treated group. Conclusions: In this group of patients in routine clinical practice who do not receive docetaxel with initial ADT, PSA response rates are significantly improved and overall dose received is higher with subsequent earlier use. However, overall survival is not significantly different between the early and later docetaxel treated patients.