Higa, Julianna L

AbstractBackgroundProstatic specific antigen (PSA) has well‐recognized limitations as a marker for treatment response and disease progression. Post hoc analysis of the PREVAIL trial reported 24.5% of chemotherapy naïve metastatic castration‐resistant prostate cancer (mCRPC) patients on enzalutamide had radiographic progression on conventional imaging with nonrising PSA. In this study, we sought to study the discordance of imaging with PSA kinetics in mCRPC patients on second generation anti‐androgens (SGA) post‐chemotherapy using combined conventional imaging, and new generation imaging in the form of C‐11 choline positron emission tomography/computed tomography (C[11] choline PET/CT) scan.MethodsWe retrospectively reviewed the medical records of 123 patients with mCRPC treated with SGA (Abiraterone or Enzalutamide) after docetaxel between 2016 and 2019. Patients underwent PSA testing, and C[11] choline PET/CT scan at baseline level before starting treatment with SGA, then every 3–6 months as part of their follow up evaluation. Loss of response to SGA was defined by increase in corrected maximum standardized uptake value (SUVmax) of pretreatment lesions on C‐11 Choline PET/CT, and/or development of new lesions. Suspicious new lesions were confirmed by biopsy and/or conventional imaging.ResultsWe identified 123 mCRPC patients who received SGA (Abiraterone, n = 106; Enzalutamide, n = 17) after docetaxel. Median duration of therapy was 13.9 months (interquartile range: 8.75–21.14). Approximately 43% (n = 53) of subjects in this study exhibited an increase in choline avidity while on SGA. Of this group, 60.4% of patients experienced a parallel rise in PSA (Group‐A), whereas 39.6% displayed a paradoxical response (PR) (Group‐B), defined as increased choline avidity combined with stable or down‐trending PSA. Median PSA at time of increase in choline avidity was 3.1 ng/ml for Group‐A, and 1.3 ng/ml for Group‐B (p = 0.0176). Median SUVmax was similar in both groups (4.9 for Group‐A, 4.6 for Group‐B; p = 0.6072). The median time for increase in choline avidity was 9.5 versus 3.9 months for Group‐A versus Group‐B, respectively (Log‐Rank = 0.0063).ConclusionNearly 40% of mCRPC patients placed on SGA post docetaxel chemotherapy will exhibit paradoxical responses to therapy, therefore, warranting close follow up with imaging. C‐11 choline PET/CT imaging is a useful tool that can help in early predication of disease progression or treatment failure.

AbstractBackgroundThe clinical course in metastatic castrate‐resistant prostate cancer (mCRPC) can be complicated when patients have disease progression after prior treatment with second generation hormone therapy (second HT), such as enzalutamide or abiraterone. Currently, limited data exist regarding the optimal choice of chemotherapy for mCRPC after failing second generation hormone therapy. We sought to evaluate three common chemotherapy regimens in this setting.MethodsWe retrospectively identified 150 mCRPC patients with disease progression on enzalutamide or abiraterone. Of these 150 patients, 92 patients were chemo‐naïve while 58 patients had previously received docetaxel chemotherapy before being started on second HT. After failing second HT, 90 patients were assigned for docetaxel‐alone (group A), 33 patients received carboplatin plus docetaxel (group B), while 27 patients received cabazitaxel‐alone (Group C). A favorable response was defined by more than or equal to 50% reduction in prostate‐specific antigen from the baseline level after a complete course of chemotherapy. Survival outcomes were assessed for 30‐month overall survival.ResultsPatients in group (B) were 2.6 times as likely to have a favorable response compared to patients in group (A) (OR = 2.625, 95%CI: 1.15‐5.99) and almost three times compared to patients in group (C) (OR = 2.975, 95%CI: 1.04–8.54) (P = .0442). 30‐month overall survival was 70.7%, 38.9% and 30.3% for group (B), (A), and (C), respectively (P = .008). We report a Hazard Ratio of 3.1 (95% CI, 1.31‐7.35; P = .0037) between patients in group (A) versus those in group (B) and a Hazard Ratio of 4.18 (95% CI, 1.58‐11.06; P = .0037) between patients in group (C) compared to those in group (B)ConclusionThis data demonstrates improved response and overall survival in treatment‐refractory mCRPC with a chemotherapy regimen of docetaxel plus carboplatin when compared to docetaxel alone or cabazitaxel alone. Further investigations are required.

e17540 Background: The clinical course in metastatic castrate-resistant prostate cancer (mCRPC) can be complicated when patients have disease progression after treatment with 2nd generation hormone therapy (2nd-HT), such as enzalutamide or abiraterone. Currently, limited data exist regarding the optimal choice of chemotherapy for mCRPC after failing 2nd-HT. We sought to evaluate three common chemotherapy regimens in this setting. Methods: We retrospectively identified 150 patients with mCRPC with disease progression on enzalutamide or abiraterone. 92 patients were chemo-naïve, while 58 patients had previously received docetaxel chemotherapy prior to 2nd-HT. After failing 2nd-HT, 90 patients received docetaxel-alone (group A), 33 patients received carboplatin plus docetaxel (group B), while 27 patients received cabazitaxel-alone (Group C). Favorable response was defined by ≥50% reduction in PSA level from baseline after a complete course of chemotherapy. Survival outcome was assessed for 30-month overall survival. Results: Mean (SD) age was 71.2 (8.28), 69.5(8.38) and 67.2 (8.36) for group (A), (B) and (C), respectively. Mean (SD) pre-chemotherapy PSA was 63.8 (138.18), 58.5 (118.15) and 53.7 (88.15) for group (A), (B) and (C), respectively. Mean (SD) Gleason score was 7.9 (1.1), 8.4 (0.88) and 8.1 (1.06) for group (A), (B) and (C), respectively. Patients in group (B) were 2.6 times more likely to have a favorable response compared to group (A) (OR = 2.625, 95%CI: 1.15 - 5.99) and almost 3 times compared to patients in group (C) (OR = 2.975, 95%CI: 1.04 – 8.54) (p-value = 0.0442). We report a Hazard Ratio (HR) of 3.1 (95% CI 1.31-7.35; p = 0.0037) between patients in group (A) versus group (B), and a HR of 4.18 (95% CI 1.58-11.06; p = 0.0037) between patients in group (C) versus group (B). Thirty-month overall survival was 70.7%, 38.9%, and 30.3% for group (B), (A), and (C) respectively (p-value = 0.008). Conclusions: Our data demonstrate improved response and cancer-specific survival in patients with treatment-refractory mCRPC on docetaxel plus carboplatin compared to docetaxel or cabazitaxel alone. Selection bias is inherent in any retrospective study; however, our finding suggests that clinicians may consider docetaxel plus carboplatin in mCRPC patients who fail 2nd-HT. Further prospective studies are warranted.