Kuker, Russ

5069 Background: Ra-223 improves the overall survival in patients with mCRPC to the bone. We assessed the safety of standard-of-care Ra-223 in combination with peposertib, a DNA-dependent protein kinase inhibitor, with or without avelumab, an anti-PD-L1 antibody. Methods: Patients with mCRPC and two or more skeletal metastases identified by bone scintigraphy with or without lymph node metastases up to 3 cm in size, but no visceral metastases, were eligible. Progression after progression after at least one androgen receptor pathway inhibitor or taxane was required. Phase 1 consisted of a two-step sequential safety lead-in using a 3+3 design. Step 1 combined 6 standard cycles of Ra-223 (55 kBq/kg), with increasing doses of peposertib: 50, 100, and 200 mg PO bid on days 3-26 of each cycle. Step 2 combined Ra-223 with the maximum tolerated dose of peposertib and added standard avelumab 800 mg IV every 14 days, starting at cycle 2 of Ra-223. Results: A total of 9 patients participated in Step 1, where the maximum tolerated peposertib dose of 200 mg PO bid with Ra-223 was deemed tolerable. A total of 6 patients participated in Step 2 and the combination of Ra-223, peposertib at 200 mg PO bid, and standard avelumab was deemed tolerable. Of the 15 patients in Phase 1, none experienced grade 4 or higher treatment-related toxicities, while 7 experienced grade 3 toxicities, including neutropenia (1), anemia (1), cardiac chest pain (1), fall (1), maculopapular rash (2), and lymphopenia (2). The median (Q1, Q3) PSA velocity from the beginning to the end of treatment was lower for Step 2 versus Step 1: 2.1 (-0.1, 4.6) versus 23.5 (18.6, 77.1) ng/mL/month (p = 0.0067). OS and PFS were calculated with the limitation that the Phase 1 was non-randomized. Median OS was not reached for Step 2, as only 1 of 6 patients had died, versus 15.2 months for Step 1, where 8 out of 9 patients had died (p = 0.0537). The patient who died in Step 2 discontinued therapy prematurely after 3 cycles due to progression and survived 15.2 months (the 5 alive completed all 6 cycles). The median radiographic PFS was 7 months for Step 2 versus 12.7 months for Step 1 (p = 0.8910). Conclusions: The combination of Ra-223 and peposertib, with or without avelumab was well tolerated. The triplet combination showed the most promising results at this early evaluation. We continue to accrue in the randomized Phase II portion of the trial. Clinical trial information: NCT04071236 .

Introduction: PET/CT is the standard-of-care for staging and therapy response assessment in lymphoma. Fluorodeoxyglucose (FDG)-avidity in extranodal marginal zone lymphoma (EMZL) remains controversial with some variability by extranodal location. The current Lugano classification recommends the use of CT scans only in staging and follow-up for EMZL. However, emerging data from small studies have challenged this suggestion. In this study we aimed to determine the ability of PET/CT to detect FDG-avid EMZL during staging work-up. Methods: First, we retrospectively analyzed the University of Miami (UM) MZL database (period 2/2016-1/2023) searching for patients who underwent staging PET/CT. Images were reviewed by expert radiologists to ascertain avidity of tumor and not surrounding tissue, with specific attention to ocular and GI locations; if scans were not available (n=15), we retrieved data from reports (results presented in part at ICML2023). Next, we aimed to validate the initial UM results additionally analyzing data from imaging reports for patients prospectively enrolled in the Lymphoma Epidemiology of Outcomes (LEO) MZL cohort (period 7/2015-5/2020), excluding LEO patients from Miami to avoid overlap. Patients with high-grade transformation at diagnosis were excluded. For patients with >1 extranodal site, each location was counted independently. We considered FDG-avid disease if SUVmax was ≥2 as this value is commonly observed between mediastinal blood pool (BP) and liver background. To normalize data, we calculated ratios of lymphoma SUVmax versus both BP and liver background, as available. Patients without measurable disease were excluded from analysis. Results: Among 210 patients with EMZL in the UM cohort, 152 had staging PET/CT and were analyzed. Twenty-two patients demonstrated >1 extranodal site providing a total of 187 locations. The LEO cohort included 411 patients from 7 centers, with 235 having available imaging reports. Fifty-two patients in this cohort demonstrated >1 extranodal site providing a total of 306 locations. Disease distribution is depicted in Table 1. Among 187 EMZL locations in the UM cohort, the most common were gastric (n=33, 17.6%), ocular (n=31, 16.6%), lung (n=30, 16%), skin and soft tissue (n=16, 8.6%, each). Similarly, lung (n=63; 20.6%), soft tissue (n=46; 15%), gastric and ocular (n=34 each; 11%) were common locations in the LEO cohort. EMZL demonstrated FDG-avidity (SUVmax ≥2) across all locations with identical values in both cohorts (UM= 78.1% & LEO= 76.5%). FDG-avidity by location is shown in Table 1A & B with salivary gland (100% & 100%), lung (93.3% & 95.2%), soft tissue (93.8% & 100%), and airways (90.9% & 100%) demonstrating high avidity in both cohorts. Contrarily, skin was commonly non-FDG avid (93.8% & 81%). The median size of FDG-avid lesions was 2.4cm (range, 0.7-17.4) in UM and 2.9cm (range, 0.1-12) in LEO cohorts. In patients with >1 extranodal site FDG-avidity was nearly universal across sites (UM=93% & LEO=100%). We observed a significant correlation between lymphoma size and FDG-avidity for UM (r=0.33; P=0.001), and for LEO (r=0.55; P<0.0001). In patients with background FDG-avidity data in the UM cohort (n=150), a BP index and liver index ≥1 detected lymphoma in 79.3% & 71.5% cases, respectively. We were unable to calculate indexes in LEO cohort since only limited data on BP (n=26) and liver (n=19) background was available in imaging reports. Conclusions: This study represents the largest analysis evaluating accuracy of PET/CT to determine initial tumor burden in 387 patients with EMZL. We demonstrate that EMZL is largely an FDG-avid disease across two cohorts, and PET/CT should be included in the staging of these patients while acknowledging possible limited sensitivity in GI locations due to physiologic uptake. Furthermore, we observed that patients with multiple extranodal locations demonstrate uniform FDG-avidity across all sites except for skin involvement. Based on our results we recommend the incorporation of PET/CT into standard staging of EMZL in planned revised Lugano classification guidelines. In those demonstrating initial FDG-avidity, a lower SUVmax threshold of SUVmax ≥2, comparison to mediastinal BP rather than to liver background activity and evaluating for resolution of focal FDG-avidity should be considered to assess treatment response in routine care and clinical trials.