Fellman, Bryan

140 Background: In the phase II EXTEND iADT omPC basket, MDT+iADT improved progression-free survival (PFS) vs iADT. Here we present the primary results of the EXTEND cADT omPC basket. We further report a pre-specified combined analysis with updated results from the iADT basket and examine the effects of MDT on immunity. Methods: Patients with 1 to 5 omPC metastases were randomized 1:1 to MDT+cADT vs cADT (NCT03599765). MDT consisted of definitive local therapy. cADT consisted of ADT +/- second-generation anti-androgens. The primary endpoint was per-protocol PFS, defined by biochemical criteria (Prostate Cancer Working Group 3), radiologic measures (RECIST v1.1), clinical progression, or death. 87 patients were needed to show superiority at a one-sided P of 0.10 by log-rank test. CDR3 regions in rearranged T cell receptor (TCR) β-chains from pre- and post-enrollment peripheral blood were sequenced with immunoSEQ (Adaptive Biotech). TCR repertoire modulation was defined as having TCR expansion plus contraction using a false-discovery-corrected betabinomial model. TCR sequencing from the ORIOLE trial (NCT02680587) was assessed for external validation. Results: From 2018 to 2022, 87 randomized patients were treated per protocol (MDT+cADT: 45; cADT: 42). 39% had castrate resistant omPC. MDT was definitive radiotherapy in all cases. With median follow-up of 31 mo, median PFS was 47 mo after MDT+cADT vs 22 mo after cADT (HR 0.50; 95% CI 0.23 to 1.08; one-sided P = 0.036). In the combined analysis (N=174) with median follow-up of 42 mo, MDT+ADT improved PFS (HR 0.45; 95% CI 0.30 to 0.69; P < 0.001), radiologic PFS (HR 0.63; 95% CI 0.40 to 0.97; P = 0.038), and castration-resistance free-survival (HR 0.40; 95% CI 0.19 to 0.82; P = 0.013). MDT+ADT had higher odds of TCR repertoire modulation vs ADT (55% vs 15%, P < 0.001). This finding was validated in the ORIOLE trial (MDT: 57% vs observation: 19%, P = 0.03). Among the subset of patients with extreme responses, random forest modeling of 37 clinical/immune variables identified TCR repertoire modulation as the variable with highest importance; further, MDT+ADT induced TCR repertoire modulation in all patients with favorable responses (i.e. PFS > 4 years) and none with unfavorable responses (i.e. PFS < 1 year). Among all patients randomized to MDT+ADT, TCR repertoire modulation was associated with longer PFS (HR 0.21; 95% CI 0.06 to 0.76; P = 0.02). Conclusions: MDT+cADT met the PFS primary endpoint of the phase II EXTEND trial, warranting phase III testing. From the combined analysis, MDT+ADT may also improve longer term outcomes including radiologic PFS and castration-resistance-free survival. Improved outcomes may result from MDT-induced immunomodulation, with implications for future trial design. Clinical trial information: NCT03599765 .

5517 Background: Uterine serous carcinoma is a less common subtype of endometrial cancer that is associated with poorer survival. The optimal post-operative adjuvant treatment strategy for these patients remains uncertain. Methods: This multi-institutional, retrospective cohort study evaluated patients with early stage uterine serous carcinoma. Patients with FIGO Stage IA-II disease after surgery, whose tumors had serous or mixed serous/non-serous histology were included. Patients with carcinosarcoma were excluded. Clinical data were abstracted from local medical records. Summary statistics, Fisher’s exact, and Kruskal-Wallis tests were used to analyze demographic and clinical characteristics. Univariable and multivariable analyses were performed for recurrence-free survival (RFS) and overall survival (OS). Results: 634 patients were included. 77% of patients had Stage IA disease, 42% showed no myometrial invasion. The majority had pure serous histology (72%) and LVSI (76%). Adjuvant treatment varied: 12% received no adjuvant therapy, 7% had chemotherapy alone, 51% had cuff brachytherapy, 12% had cuff brachytherapy with chemotherapy (cuff/chemo), and 19% underwent pelvic radiation (EBRT). Complete RFS and OS data were available for 607 and 609 patients, respectively, and the median follow-up time was 58 months. As compared with patients who received no adjuvant therapy, patients who received cuff or cuff/chemo had improved RFS (cuff: HR 0.70, p = 0.02; cuff/chemo HR 0.53, p = 0.01) and OS (cuff HR 0.56, p = 0.001; cuff/chemo HR 0.48, p = 0.01). In a direct comparison, patients with cuff/chemo had better RFS and OS than those with chemotherapy alone (RFS HR 0.52, p = 0.03; OS HR 0.50, p = 0.05). There were no differences in RFS or OS for women who received chemotherapy alone or EBRT. Improved survival with cuff and cuff/chemo persisted on multivariable analyses (included age, stage, LVSI, adjuvant therapy type); additionally, EBRT was also associated with improved OS. In analyses limited to patients without myometrial invasion, patients with cuff or cuff/chemo had improved RFS and OS compared with observation alone. Conclusions: The use of adjuvant cuff brachytherapy with and without chemotherapy was associated with improved RFS and OS in patients with early stage uterine serous carcinoma.

Objective To evaluate how many patients could have undergone partial nephrectomy ( PN ) rather than radical nephrectomy ( RN ) before and after neoadjuvant axitinib therapy, as assessed by five independent urological oncologists, and to study the variability of inter‐observer agreement. Patients and Methods Pre‐ and post‐systemic treatment computed tomography scans from 22 patients with clear cell renal cell carcinoma in a phase II neoadjuvant axitinib trial were reviewed by five independent urological oncologists. R.E.N.A.L. nephrometry score and κ statistics were calculated. Results The median R.E.N.A.L. nephrometry score changed from 11 before treatment to 10 after treatment ( P = 0.002). Five tumours with moderate complexity before axitinib treatment remained moderate complexity after treatment. Of 17 tumours with high complexity before axitinib treatment, three became moderate complexity after treatment. The overall κ statistic was 0.611. Moderate‐complexity κ was 0.611 vs a high‐complexity κ of 0.428. Before axitinib treatment the κ was 0.550 vs 0.609 after treatment. After treatment with axitinib, all five reviewers agreed that only five patients required RN (instead of eight before treatment) and that 10 patients could now undergo PN (instead of three before treatment). The odds of PN feasibility were 22.8‐times higher after treatment with axitinib. Conclusions There is considerable variability in inter‐observer agreement on the feasibility of PN in patients treated with neoadjuvant targeted therapy. Although more patients were candidates for PN after neoadjuvant axitinib therapy, it remains difficult to identify these patients a priori .