Citations

10007 Background: The NCI-Children’s Oncology Group (COG) Pediatric Molecular Analysis for Therapy Choice (MATCH) trial assigns patients aged 1-21 years with relapsed or refractory solid tumors, CNS tumors, lymphomas, and histiocytic disorders to phase 2 treatment arms of molecularly-targeted therapies based on genetic alterations in their tumor. Arm B (APEC1621B) evaluated the orally bioavailable FGFR inhibitor erdafitinib in patients whose tumors harbored activating alterations in FGFR 1/2/3/4. Methods: Patients received oral erdafitinib 4.7 mg/m 2 /dose (Max dose: 8 mg) daily for 28-day cycles until disease progression or drug related dose limiting toxicity (Max 26 cycles). Disease assessments were performed every 2-3 cycles. The primary endpoint was objective response rate; secondary endpoints included progression free survival (PFS). Results: A total of 20 evaluable patients (median age: 15 yrs) were enrolled from June 2018 to July 2022 in this first study of erdafitinib in pediatric patients. The most common diagnosis (n = 17) was glioma or glioneuronal tumor (11 low grade and 6 high grade). Three patients had non-CNS solid tumors (1 each with neuroblastoma, osteosarcoma, and rhabdomyosarcoma). FGFR alterations detected consisted of activating hotspot mutations in FGFR1 (n = 16), FGFR2 (n = 1), FGFR4 (n = 1), and FGFR1 fusions (n = 2; FGFR1: TACC1, FGFR1: TACC3). Partial responses were confirmed by central review in 2/20 patients (10%, 90%CI: 3.4%, 26.2%), both with low grade gliomas or glioneuronal tumors (LGG, LGGNT) and FGFR1 hotspot mutations (K687E and N577K). A best response of stable disease (SD) was observed in 6 additional patients with gliomas with a median duration of SD of 6.5 cycles. Six-month PFS was 45% (95% CI: 23.1%, 64.7%) and six-month OS was 89.7% (95%CI: 64.8%, 97.3%). Treatment related adverse events included those previously reported with FGFR inhibitors including hyperphosphatemia and nail changes or infections. Grade 1 vision changes were also reported. There was one Grade 3 spinal cord compression and one Grade 4 intracranial hemorrhage. Conclusions: Erdafitinib was generally well tolerated in this heavily pre-treated cohort of children with relapsed tumors harboring FGFR alterations. Partial responses or stable disease were observed in the majority (6/11, 54%) of patients with FGFR1-mutant low grade gliomas or glioneuronal tumors, suggesting the possible benefit of FGFR inhibitor therapy for these patients. Further studies would be necessary to more thoroughly evaluate the activity of erdafitinib for patients with other histologies and FGFR alteration types or combination approaches that include other targeted and/or cytotoxic agents. Clinical trial information: NCT03210714 .

TPS8064 Background: Multiple myeloma (MM) remains an incurable disease. Combinations of established agents, including proteasome inhibitors (PIs), immunomodulatory drugs (IMiDs), and anti-CD38 antibodies, are used in all lines of therapy, but re-exposure to previously received classes of therapy is associated with decreasing response rates and duration of response (Moreau et al. 2021). BCMA-targeted agents have recently been approved for the treatment of patients with RRMM whose disease has been exposed or become refractory to PIs, IMIDs and anti-CD38 antibodies (triple-class exposed or refractory MM). Although effective, the majority of patients who respond to anti-BCMA agents eventually relapse. Proven salvage therapies for these patients are currently lacking and represent a new unmet medical need. Cevostamab is an immunoglobulin G1-based T-cell-engaging bispecific antibody that targets Fc receptor-homolog 5 (FcRH5) on myeloma cells and CD3 on T cells. Dual binding results in T-cell activation and potent killing of MM cells. In an ongoing Phase I study (GO39775; NCT03275103), cevostamab monotherapy showed promising activity in heavily pre-treated patients with RRMM, including those with prior exposure to anti-BCMA agents (Trudel et al. 2021). Methods: CAMMA 2 (CO43476; NCT05535244) is an open-label, multicenter Phase I/II trial evaluating cevostamab monotherapy in patients with RRMM who are triple-class refractory and have previously received an anti-BCMA agent. Prior anti-BCMA antibody-drug conjugates or chimeric antigen receptor (CAR) T cells are permitted in Cohorts A1 and B1, while prior anti-BCMA bispecific antibodies are allowed in Cohorts A2 and B2. In A1 and A2, cevostamab is administered by intravenous infusion and is initiated with step dosing (0.3mg on Cycle [C] 1 Day [D] 1 and 3.3mg on C1D2, D3, or D4 depending on the emergence and resolution of cytokine release syndrome [CRS] after the initial administration), with the target dose of 160mg given on C1D8 and on D1 of each subsequent 21-day cycle. Patients are hospitalized for the C1 administrations only and treatment is continued until disease progression or unacceptable toxicity occurs. CRS is managed per protocol based on the clinical presentation and may involve corticosteroid and tocilizumab treatment. Primary objectives are evaluation of efficacy (primary endpoint: objective response rate by investigator assessment using IMWG criteria) and safety. Secondary objectives include assessment of quality of life, pharmacokinetics, pharmacodynamics, and immunogenicity. Cohorts B1 and B2 will evaluate the efficacy and safety of cevostamab at the recommended Phase II dose in this setting. As of February 2023, enrolment into Cohorts A1 and A2 is ongoing. Clinical trial information: NCT05535244 .

7514 Background: Pirtobrutinib is a highly selective, non-covalent (reversible) BTKi. Here, we report updated results of pirtobrutinib in patients (pts) with cBTKi pre-treated relapsed/refractory (R/R) MCL and more than 3 years follow-up from start of enrollment. Methods: Pts with cBTKi pre-treated R/R MCL received pirtobrutinib monotherapy in a multicenter phase 1/2 BRUIN trial (NCT03740529). Efficacy was assessed in the prespecified primary efficacy cohort that comprised the first 90 enrolled pts who had measurable disease, had received a prior cBTKi, and had no known central nervous system involvement. The primary endpoint was overall response rate (ORR) as assessed by independent review committee. Secondary endpoints included duration of response (DOR) and safety. A data cut of 29 July 2022 was utilized. Results: Among MCL pts who received a prior cBTKi (n=90), median age was 70 years (range, 46-87), median prior lines of therapy were 3 (range, 1-8), 82% discontinued a prior cBTKi due to disease progression, and 78% had intermediate/high risk sMIPI score. Of samples available, 17/36 (47%) had TP53 mutations and 25/34 (74%) had Ki67 ≥30%. The ORR was 57% (95% CI, 46-67), including 19% complete responses (n=17) and 38% partial responses (n=34). At a median follow-up time of 13 months, the median DOR among the 51 responding pts was 17.6 months (95% CI, 7.3-27.2). The 12- and 18-month estimated DOR rates were 58% (95% CI, 41-72) and 45% (95% CI, 27-61), respectively. ORR and DOR by subgroups are shown in the Table. The median progression-free survival was 7.4 months (95% CI, 5.3–13.3). The median overall survival was 23.5 months (95% CI, 15.9-NE). In the MCL safety cohort (n=166), the most frequent treatment-emergent adverse events (TEAE) were fatigue (31%), diarrhea (22%), and anemia (17%). The most common Grade ≥3 TEAE was neutropenia (15%). Grade ≥3 TEAE of hemorrhage (3%) and atrial fibrillation/flutter (2%) were infrequent. Only 5 (3%) pts discontinued due to a treatment-related AE. Conclusions: Pirtobrutinib continues to show durable efficacy and a favorable safety profile in heavily pre-treated R/R MCL pts with prior cBTKi therapy. Responses were observed in pts with high-risk disease features including pts with blastoid/pleomorphic variants, elevated Ki67 index, and TP53 mutations. Clinical trial information: NCT03740529 . [Table: see text]

TPS7073 Background: Despite improved outcomes with azacitidine (AZA) and venetoclax (VEN) in frontline unfit AML (CR 37% and CR/CRi 66%), long-term survival for these patients remains inadequate (mOS < 15m, DiNardo NEJM 2020). CD123 is expressed on the majority of AML blasts and leukemic stem cells while minimally expressed on normal hematopoietic stem cells (Kovtun Blood Adv 2018). Pivekimab sunirine (PVEK, IMGN632) is an antibody-drug conjugate (ADC) comprising a high-affinity CD123 antibody, cleavable linker, and an indolinobenzodiazepine pseudodimer (IGN) payload. The IGN payload alkylates DNA and causes single strand breaks without crosslinking. IGNs are designed to have high potency against tumor cells, while demonstrating less toxicity to normal marrow progenitors than other DNA-targeting payloads. Clinical data in relapsed/refractory (R/R) AML (Daver ASH 2022) supported the continued clinical exploration of the PVEK+AZA+VEN triplet. The current enrolling dose expansion cohorts (Regimen C; Cohorts 1 and 2) in frontline AML will evaluate antileukemia activity and MRD levels in the combination of PVEK+AZA+VEN. Regimen E will enroll patients with R/R AML to evaluate the safety and antileukemia activity of PVEK in combination with magrolimab. Methods: This is an open-label, multicenter, Phase 1b/2 study of PVEK administered in combination regimens in patients with frontline and R/R CD123-positive AML. Patients will receive the established recommended phase 2 dose (RP2D) of PVEK 0.045 mg/kg IV, as a < 30-minute outpatient infusion. In Regimen C, patients will receive PVEK 0.045 mg/kg IV on D7 + azacitidine 75 mg/m 2 SC or IV daily on days 1 to 7, and venetoclax up to 400 mg PO daily for at least 14 days (Cohort 1) or for up to 28 days (Cohort 2) in a 28-day cycle. In Regimen E, R/R AML patients will receive PVEK 0.045 mg/kg IV on D1 of the 28-day cycle in combination with magrolimab at 30 mg/kg Q2W, after the standard ramp up schedule. Regimen C will enroll adults with untreated AML, CD123+ by flow cytometry or IHC and no prior HMA treatments. The primary endpoints for Regimen C are composite CR rate, overall response rate (ORR), duration of remission (DOR), MRD levels and key secondary endpoints are safety, PK and immunogenicity. Regimen E will enroll adult patients with relapsed or refractory CD123+ AML with up to 2 prior lines of therapy. The primary endpoint for Regimen E is dose limiting toxicities (DLTs) and key secondary endpoints are safety, antileukemic activity, PK and immunogenicity. The PVEK+AZA+VEN triplet (Regimen C) is currently enrolling frontline unfit patients across sites in France, Germany, Italy, Spain, UK and USA. The PVEK+Magro doublet (Regimen E) is planned to be open for enrollment mid-2023 at sites in the USA. Clinical trial information: NCT04086264 .

7006 Background: Older adult patients (pts) with Philadelphia-chromosome-negative (Ph-) acute lymphoblastic leukemia (ALL) have poor survival with chemotherapy. The α-CD22 Ab-drug conjugate inotuzumab ozogamicin (InO) and α-CD19/CD3 T-cell engager blinatumomab (blina) were each superior to chemotherapy in Phase III studies in relapsed/refractory B-ALL. Because InO induces high CR rates and blina can induce durable remissions in low burden disease, we conducted a Phase II trial of induction InO then blina for older adults with newly-diagnosed (ND), Ph-, B-ALL. Methods: Eligible were pts ≥60 years old with ND, Ph-, CD22+ (≥20% of blasts) B-ALL without plan for allogeneic HCT (alloHCT). Pts with CNS leukemia or liver disease were excluded. Induction IA was InO 0.8 mg/m 2 day (d) 1, 0.5 mg/m 2 d8, d15 IV on a 21d cycle. Pts with adequate cytoreduction (marrow blasts by ≥50% or cellularity ≤20%) after IA went to IB if in CR/CRi (InO 0.5 mg/m 2 d1, d8, d15 IV; 28d cycle) or IC if no CR/CRi (InO 0.8 mg/m 2 on d1 and 0.5 mg/m 2 on d8 and d15 IV; 28d cycle). Those without cytoreduction to IA started course II blina. Pts without events in IA/B/C received course II blina CIV (9 mcg/d x 7d then 28 mcg/d x 21d; 14d break; 28 mcg/d x28d). Pts with CR/CRi to InO received 2 more 28d cycles of blina, others received 3 more. CNS prophylaxis was methotrexate 15 mg intrathecal x 8. The primary endpoint was 1-yr event-free survival (EFS) with a lower limit of a 90% CI for 1-yr EFS >10% defined as success. EFS was the time from therapy start to failure to achieve CR/CRh/CRi by end Course II, progression, relapse, or death, whichever occurred first. Results: Thirty-three eligible pts were treated (1 ineligible, 2 nd malignancy). The median age was 71 years (range 60-84). Median WBC count was 3,200/mcl (range 6-38,000). Median CD22 expression was 92% (range 21-100%). Eight pts had therapy-related ALL. The cumulative CR rates through Course IA/B/C and Course II were 85% and 97%, respectively (Table). With median follow up of 22 mo, the 1-yr EFS was 75% (95% CI 61-92%). The 2-sided 90% CI was 63-89% for 1-yr EFS with lower bound above 10% indicating regimen success. Twelve pts had events: 9 relapses, 2 deaths in remission (1 after alloHCT), and 1 death without remission from respiratory failure with sinusoidal occlusion syndrome of liver. The 1-yr OS was 84% (95% CI 72-98%). Nine pts have died, 6 after relapse. Conclusions: InO induction then blina consolidation is highly active for ND, Ph-, CD22+ B-ALL. The regimen is an option for older adults and a comparator regimen for future studies. Support: U10CA180821, U10CA180882, U10CA180820 https://acknowledgments.alliancefound.org . Clinical trial information: NCT03739814 . N=33 I A/B/C II Composite CR* 28 ( 85%) 32 ( 97%) CR 15 (45%) 19 (58%) CRh 11 (33%) 12 (36%) CRi 2 (6%) 1 (3%) Refractory 3 (9%) † - 1-yr EFS 75% (95% CI 61-92%) 1-yr OS 84% (95% CI 72-92%) *CR+CRh+CRi † 1 completed IA only

PURPOSE The standard of care for locally advanced rectal cancer in North America is neoadjuvant pelvic chemoradiation with fluorouracil (5FUCRT). Neoadjuvant chemotherapy with fluorouracil and oxaliplatin (FOLFOX) is an alternative that may spare patients the morbidity of radiation. Understanding the relative patient experiences with these options is necessary to inform treatment decisions. METHODS PROSPECT was a multicenter, unblinded, noninferiority, randomized trial of neoadjuvant FOLFOX versus 5FUCRT, which enrolled adults with rectal cancer clinically staged as T2N+, cT3N–, or cT3N+ who were candidates for sphincter-sparing surgery. Neoadjuvant FOLFOX was given in six cycles over 12 weeks, followed by surgery. Neoadjuvant 5FUCRT was delivered in 28 fractions over 5.5 weeks, followed by surgery. Adjuvant chemotherapy was suggested but not mandated in both groups. Enrolled patients were asked to provide patient-reported outcomes (PROs) at baseline, during neoadjuvant treatment, and at 12 months after surgery. PROs included 14 symptoms from the National Cancer Institute's Patient-Reported Outcomes version of the Common Terminology Criteria for Adverse Events (PRO-CTCAE). Additional PRO instruments measured bowel, bladder, sexual function, and health-related quality of life (HRQL). RESULTS From June 2012 to December 2018, 1,194 patients were randomly assigned, 1,128 initiated treatment, and 940 contributed PRO-CTCAE data (493 FOLFOX; 447 5FUCRT). During neoadjuvant treatment, patients reported significantly lower rates of diarrhea and better overall bowel function with FOLFOX while anxiety, appetite loss, constipation, depression, dysphagia, dyspnea, edema, fatigue, mucositis, nausea, neuropathy, and vomiting were lower with 5FUCRT (all multiplicity adjusted P < .05). At 12 months after surgery, patients randomly assigned to FOLFOX reported significantly lower rates of fatigue and neuropathy and better sexual function versus 5FUCRT (all multiplicity adjusted P < .05). Neither bladder function nor HRQL differed between groups at any time point. CONCLUSION For patients with locally advanced rectal cancer choosing between neoadjuvant FOLFOX and 5FUCRT, the distinctive PRO profiles inform treatment selection and shared decision making.

5088 Background: Previous evidence suggests that there may be no additional benefit of triplet therapy in low volume disease based on limited data. Therefore, we investigated the efficacy of triplet therapy as compared to docetaxel (D) and androgen pathway inhibitor (API) doublets by volume of disease using the most up to date results from the ARASENS trial. Methods: Phase III randomized controlled trials (RCTs) assessing treatment intensification with API, and/or D in patients with mCSPC were included. Precomputed hazard ratios (HR) with 95% confidence intervals (CI) for OS were pooled using an inverse-variance approach. A DerSimonian-Laird random-effects meta-analysis was conducted to assess the efficacy of triplet therapy compared to D doublet therapy. P-value of interaction was computed to assess difference between high (HV) and low volume (LV) disease subgroups (Pint <0.1 - statistical significance). Additionally mixed treatment comparisons were computed using network meta-analysis (NMA) to assess the comparative effectiveness of triplet therapy compared to API doublets by volume of disease. Results: Pairwise meta-analysis included a total of 3 RCTs (ARASENS, PEACE-1, ENZAMET) with 2518 patients (HV: 1820; LV: 698) as shown. In patients with HV disease, 385 (43%) and 484 (53%) deaths were observed with triplet therapy, and D doublet, respectively. Triplet therapy significantly improved OS as compared to D doublet in HV (HR: 0.73; 95% CI: 0.64-0.84). In patients with LV disease, 73 (20%) and 94 (28%) deaths were observed with triplet therapy, and D doublet, respectively. Triplet therapy significantly improved OS as compared to D doublet in LV (HR: 0.71; 95% CI: 0.52-0.97). There was no statistically significant interaction by volume of disease for triplet therapy vs. D doublet (Pint: 0.86). NMA including 10 clinical trials and over 11500 patients updated as of 13th Feb 2023 showed that in HV mCSPC, triplet therapy was ranked as potentially the most efficacious treatment option and may improve OS compared to API doublet therapy (HR: 0.83; 95% CI: 0.66-1.03). In LV mCSPC, API doublet therapy was ranked as potentially the most efficacious treatment followed by triplet therapy. There was no significant difference between triplet therapy and API doublet therapy (HR: 1.12; 95% CI: 0.74-1.12). Conclusions: These results underscore that triplet therapy may be preferred in mCSPC patients with HV disease whereas API doublet therapy may be preferred in LV disease. [Table: see text]

4541 Background: PROSPER is a phase 3 National Clinical Trials Network study that accrued pts with clinical stage ≥T2 or TanyN+ RCC of any histology planned for radical/ partial nephrectomy. Pts were randomized to perioperative nivo followed by primary tumor resection and 9 cycles of nivo postoperatively or standard surgery followed by observation. To address concerns that core kidney bx might 1) not provide accurate diagnosis and 2) delay surgery due to adverse events (AEs) or scheduling, the study was amended from requiring all patients to undergo core bx prior to treatment for confirmation of RCC, to only require bx in patients randomized to the nivo arm. Herein, we report the accuracy and safety of primary tumor core bxs in predicting final histology and nuclear grade by both site and central pathology review as well as time from enrollment to surgery. We also report AEs of preoperative nivo. Methods: Concordance of both core bx and primary tumor by site and central pathology review of histology and grade (1-2 vs 3-4) are reported, along with the Cohen’s Kappa value, which measures the agreement and concordance (kappa=0 is no concordance and 1 is highest). AEs relating to core bxs and preoperative nivo, as well as time from enrollment to surgery for each arm, comparing pre- and post-amendment (dropping bx requirement in surgery alone arm) are also reported. Results: 387/404 pts in the nivo arm and 171/415 pts in the surgery alone arm had core bxs. 632 patients had both central pathology and site review available. 41 of all randomized patients (819) were considered as non-RCC and 26/41 were identified via bx. The median times from enrollment to surgery for nivo and control arms pre-amendment were 32d vs 19 d, and post-amendment were 21 d vs 14 d, respectively. The median (25th-75th percentile) number of days from last preoperative nivo to surgery was 14 d (9-20). AEs related to core bx, generally from bleeding, were reported in 13/558 (2.3%) pts. 2/13 bxs resulted in life-threatening complications. 21/353 (6%) of pts receiving nivo pre-surgery had ≥ grade 3-5 AE attributed to nivo. 181/353 (51%) pts had any grade AE attributed to nivo. Concordance between bxs and primary tumor pathologies for determining histological subtype was Kappa = 0.62. Agreement between central pathology and originating site review of primary tumor for determining nuclear grade was Kappa = 0.56, and concordance of histology was Kappa = 0.78. Conclusions: The PROSPER trial use of core bxs in advance of neoadjuvant therapy was generally safe, largely consistent with primary tumor histology and grade, and did not delay resection of the primary tumor. AEs of preoperative nivo were consistent with nivo AEs in metastatic disease. This approach is valid for future neoadjuvant trials. Clinical trial information: NCT03055013 .

e16259 Background: Patients with KRAS mutant (mt) pancreatic ductal adenocarcinoma (PADC) have worse survival outcomes compared to KRAS wild-type (wt) PDAC patients. However, the prognostic implication of the KRAS mutation subtype (e.g. G12D, G12R, G12V and Q61) remains unclear. Furthermore, the clinical and molecular characteristics associated with these mutation subtypes remain not well defined. Methods: A retrospective review was conducted on patients with KRAS PDAC who underwent Next Generation Sequencing at Mayo Clinic between December 1, 2018 and December 1, 2021. Their somatic mutations, RNA expression, demographics, disease characteristics, therapies offered, and clinical outcomes were collected via chart review. Results on KRAS wt were reported previously; KRAS mt are reported here. Results: A total of 158 KRAS mt patients (at diagnosis: average age 63.8 years, 57% male, 88 (56%) Stage IV) were included. 10% of patients had KRAS Q61 mutation, 14% G12R, 30% G12V and 46% G12D. G12R had a longer overall survival (OS) compared to the others (median 24.8 vs 17.5 months, unadjusted hazard ratio (HR) 0.68, p=0.05), particularly in patients with localized disease at diagnosis (median 35.4 vs 28.3 months, p=0.08). Among patients with metastatic disease at diagnosis, G12V had the lowest OS (median 9.8 vs 12.4 months, unadjusted HR 1.8, p=0.02). 137 (87%) patients had at least one pathogenic somatic variant, with statistically significant differences in SMAD4, TP53, MYC, RB1, KMT2D, RBM10, RNF43, KDM6A, KMT2C, RBM10, LRP1B, PIK3CA, and SMARC among the KRAS mt subtypes. 82 (52%) patients had at least one RNA expression variant, with statistically significant differences in CCND1, CCNE1, HRAS, MET, EGFR, and ERB3 among KRAS mt subtypes. Between these subtypes, there were no statistically significant differences in TMB value, location of PDAC or subsequent metastasis, lines of treatment (average 2.3), age at diagnosis, or gender. Conclusions: KRAS mt subtypes may confer different PDAC phenotypes. In our cohort, G12R is associated with improved OS while G12V correlates with worse prognosis in de novo metastatic disease. Additionally, there are differences in genomic variations and RNA expression between the KRAS mt subtypes. To further examine this, transcriptomic analysis is underway. [Table: see text]

4009 Background: Oncogenic FGFR2 alterations (fusions/rearrangements (f/r), amplifications, mutations) represent a broad therapeutic opportunity as they drive multiple solid tumors, particularly cholangiocarcinoma (CCA). However, off-isoform toxicity and on-target resistance limit the benefit of approved pan-FGFR inhibitors (FGFRi). RLY-4008 is the first potent, highly selective, oral FGFR2 inhibitor designed to overcome these limitations by targeting FGFR2 driver alterations and resistance mutations. Here, we present updated dose escalation results from ReFocus (NCT04526106), a seamless Phase I/II, open label study evaluating the safety and preliminary efficacy of RLY-4008 in patients (pts) with advanced, FGFR2-altered solid tumors. Methods: Adult pts received RLY-4008 BID, QD, QD discontinuous on a 4-week (wk) cycle following a Bayesian Optimal Interval design. Treatment-related adverse events (TRAEs), PK, ctDNA and anti-tumor activity (RECIST v1.1) were assessed. Results: As of 30 Jan 23, 116 pts (82 f/r, 27 mutation, 6 amplification) received RLY-4008 at doses of 20-200 mg/day, including 91 with CCA. 50% had prior FGFRi, and median lines of prior therapies was 3 (1-15). 28/46 ct-DNA-evaluable pts with CCA with prior FGFRi had ≥1 baseline resistance mutation, most commonly at FGFR2 N549X (23/46) or V564X (17/46). RLY-4008 had favorable PK with doses ≥40 mg QD providing FGFR2 occupancy ≥90%. 70 mg QD was the RP2D based on PK, safety, anti-tumor activity and exposure-dependent tumor regressions in FGFRi-naïve CCA f/r pts. Anti-tumor activity was observed in CCA and solid tumors across doses and FGFR2 alterations with radiographic tumor reductions in 74 (64%), SD/PR in 83 (72%), including 4/4 (100%) FGFRi-naïve CCA f/r pts at RP2D achieving confirmed PR. Clinically meaningful disease control and durable responses were observed in pts with FGFR2 f/r CCA. Overall, median treatment duration was 24 wks (range <1-108 wks). 105 pts discontinued (PD (81%), AE (3%), other (7%)). Across doses, most common TRAEs were low-grade PPE (57%), stomatitis (56%), dry mouth (38%), alopecia (28%), and dry eye (22%). No grade 4/5 TRAEs were observed. Conclusions: These encouraging dose escalation data confirm the broad therapeutic potential of highly selective FGFR2 targeting with RLY-4008 by demonstrating encouraging initial efficacy across FGFR2-altered solid tumors and genomic alterations, with a differentiated safety profile that avoids FGFR1- and FGFR4-related toxicity. Phase 2 of ReFocus continues across solid tumors and with registrational intent in FGFRi-naïve, FGFR2 f/r CCA. Clinical trial information: NCT04526106 . [Table: see text]