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TPS10628 Background: Despite advances in cancer treatment, a lack of established population-level cancer screening strategies for early detection across cancer types contributes to cancer-related mortality. Emerging MCED liquid biopsy tests represent a screening approach with potential to enable detection of multiple malignancies at earlier stages in the disease process. We previously showed that an initial classifier based on a genome-wide methylome enrichment platform detected 12 cancer types, including early-stage, low-shedding tumors (Park et al. AACR 2023. Abs 1030). However, clinical performance of the platform has not been evaluated prospectively. Thus, the CAMPERR study (NCT05366881) was designed to train and validate a cell-free methylated DNA immunoprecipitation and high throughput sequencing (cfMeDIP-seq)-based test for detection and differentiation of 20 pre-selected cancer types, representing 93% of annual cancer incidence and 88% of annual cancer deaths. Longitudinal follow-up for a subset of participants with lung cancer will enable training and validation for MRD-based recurrence prognostication. Methods: This case-control study is enrolling participants with 20 different pre-specified cancer types (n=2400) and those without known cancer (n=3900). Eligible participants are ≥40 years of age and not receiving treatment for cancer at the time of enrollment or taking any demethylating/hypomethylating agents. Cases include individuals with newly diagnosed (≤120 days), untreated cancer or recurrence of a cancer originally diagnosed >5 years ago. Cancers of interest are stage I-IV bladder, brain, breast, cervical, colorectal, endometrial, esophageal, gastric, head and neck, hepatobiliary, leukemia, lung, lymphoma, multiple myeloma, ovarian, pancreatic, prostate, renal, sarcoma, and thyroid. Participants with stage I-III lung cancer will have clinical follow-up and blood draws after completion of first-line treatment, every 3 mo for the first year thereafter, and every 6 mo for an additional 2 years. Eligible control participants have not been diagnosed with invasive cancer in the last 5 years and will have clinical follow-up ≥12 mo from enrollment to evaluate cancer status. Liquid biopsy results will not be returned to clinicians or participants. The primary objective is cancer detection. Secondary objectives include detection of specific cancer types, identification of the tissue of origin, and prognostication of clinical outcomes (eg, recurrence-free survival, overall survival). CAMPERR is currently enrolling at 15 sites. As of December 3, 2025, 2108 of 2400 cancer cases have been enrolled, including prostate (n=225), lung (n=216), colorectal (n=211), breast (n=193), and pancreatic (n=192); controls are fully enrolled. Clinical trial information: NCT05366881 .

e19543 Background: Multiple myeloma (MM) is a plasma cell malignancy characterized by immune dysfunction and end-organ damage. Emerging preclinical evidence suggests vitamin D is implicated in MM biology through effects on plasma cell differentiation and immune regulation. Vitamin D deficiency is common among patients with MM, yet its prognostic significance remains unclear. Clarifying its role may inform risk stratification and supportive management in MM. Methods: We conducted a retrospective cohort study using the multicenter TriNetX research network. Adults aged ≥20 years diagnosed with MM between 2011 and 2024 were included. Vitamin D status was defined using serum 25-hydroxyvitamin D levels, with deficiency defined as ≤30 ng/mL and normal levels defined as 31–80 ng/mL. Patients were stratified into two groups based on vitamin D status at the time of MM diagnosis. Propensity score matching (1:1) was performed to balance age, sex, race, baseline laboratory values, and clinically relevant comorbidities between groups. Kaplan–Meier survival analyses and Cox proportional hazards models were performed for outcome analyses. Results: A total of 36,273 patients with MM were included, of whom 42% (n = 15,262) had vitamin D deficiency. After propensity score matching, 14,023 vitamin D–deficient patients were well balanced with 14,006 non-deficient patients across baseline characteristics. In the matched cohort, the mean age was 64 years, 49% were female, and 64% were White. At five years, vitamin D deficiency was associated with a significantly higher risk of mortality (hazard ratio [HR] 1.63, 95% CI 1.54–1.72), with lower five-year overall survival (OS) compared with non-deficient patients (71.1% vs 80.8%, p<0.05). Vitamin D deficiency was also associated with increased risks of pneumonia (risk ratio [RR] 1.11), bacteremia (RR 1.22), and critical care admission (RR 1.30) (all p<0.05). Additionally, deficient patients had higher risks of acute kidney injury (AKI) (RR 1.19) and venous thromboembolism (RR 1.18) (both p<0.05). Notably, the risk of MM relapse was modestly increased among vitamin D-deficient patients (RR 1.07, 95% CI 1.01–1.13). No significant associations were observed between vitamin D deficiency and amyloidosis or pathologic fractures. In multivariable Cox regression, vitamin D deficiency remained independently associated with worse five-year OS (adjusted HR 1.60, 95% CI 1.52–1.67). Conclusions: This study highlights the negative impact of vitamin D deficiency in patients with MM. It identifies a high-risk subgroup of patients characterized by worse five-year OS, higher rates of serious infections, AKI, critical care utilization, and an increased risk of MM relapse. These findings suggest vitamin D deficiency as a clinically relevant prognostic marker in MM. Prospective studies are warranted to determine whether vitamin D level optimization can improve MM outcomes.

e19536 Background: Chronic kidney disease (CKD) may impair physiologic resilience during chimeric antigen receptor (CAR) T-cell therapy for multiple myeloma (MM). While cytokine response syndrome (CRS) and immune cell-associated neurotoxicity syndromes (ICANS) have been described in MM CAR-T recipients with CKD, the broader cardiopulmonary, infectious, renal, and economic implications of CKD remain insufficiently defined. We examined the national impact of CKD on mortality, immune cell effector toxicities, organ dysfunction, infections and resource utilization. Methods: Adult MM hospitalizations receiving CAR T-cell therapy were identified from the National Inpatient Sample (2018–2022) using ICD-10-PCS codes. Patients with ESRD were excluded. CKD was categorized as CKD3a+ (eGFR <60 mL/min) versus no CKD/CKD1–2. Outcomes included in-hospital mortality, CRS (2021–2022), ICANS (2022), cardiac arrhythmias, acute kidney injury (AKI), renal replacement therapy, respiratory failure, infections and total hospitalization cost (calculated using TOTCHG variable and adjusted cost to charge ratio). Comparative analysis was done using chi-square testing. Multivariate analysis adjusted for demographics, comorbidities, and hospital characteristics. Results: Among 2,045 weighted MM CAR-T hospitalizations, 7.6% had CKD3a+. Overall CRS rates were similar (66.7% vs 64.9%; p=0.839) between CKD3a+ vs no/CKD1-2. Overall ICANS rates were also comparable (16.7% vs 17.3%; p=0.941). Differences in CRS/ICANS grades were not significant. CKD3a+ patients experienced sharply higher AKI (58.1% vs 13.0%; p<0.001; adjusted odds ratio [OR] 9.2, p<0.001). Renal replacement therapy was more frequent in CKD3a+ but non-significant (3.2% vs 0.8%; p=0.196). Acute respiratory failure was more frequent (9.7% vs 2.9%; p=0.045) in patients with CKD. Cardiac arrhythmias were numerically higher but non-significant (25.8% vs 20.6%; p=0.527; adjusted OR 1.3, 95% CI 0.4–4.9; p=0.673). Infections were amplified, including gram-negative bacteremia (3.2% vs 0.3%; p=0.026), sepsis (9.7% vs 2.6%; p=0.040), and septic shock (3.2% vs 0.3%; p=0.027) in patients with CKD. Inpatient mortality was numerically higher (6.5% vs 1.9%; p=0.101), though nonsignificant after adjustment (OR 6.9; p=0.319). Hospital costs were substantially higher in CKD3a+ (USD 346,769 vs 239,175; p=0.006), though not significant in adjusted models (OR 1.3; p=0.120). Conclusions: CKD3a+ is associated with markedly increased AKI, higher respiratory failure and infections, with a trend towards higher hospitalization costs. Inpatient mortality, CRS and ICANS rates were similar. CKD3a+ represents a significant vulnerability that amplifies downstream complications in MM CAR-T recipients, warranting enhanced pre-treatment risk stratification, infection surveillance and renal-preserving strategies.

e15647 Background: Colorectal cancer (CRC) screening offers an opportunity to prevent invasive disease by detecting and removing precancerous lesions. Colonoscopy-based detection of adenomas and serrated polyps is strongly associated with reduced risk of interval CRC. While the performance of noninvasive CRC screening tests is well described, comparative evidence on adenoma detection across screening colonoscopy and stool-based strategies with follow-up colonoscopy remains limited. We conducted a systematic review to compare adenoma detection across CRC screening modalities. Methods: MEDLINE (PubMed) and Embase were searched from January 1, 2000, through July 10, 2025, for peer-reviewed, U.S.-based studies reporting colonoscopy among average-risk adults aged ≥45 years, who underwent screening colonoscopy or follow-up colonoscopy after a positive stool-based screening test [fecal immunochemical test (FIT) or multi-target stool DNA (mt-sDNA) test]. The primary outcome was the detection of one or more adenomas at colonoscopy. High-risk or surveillance cohorts, AI-assisted colonoscopy, diagnostic accuracy trials, and non-U.S. studies were excluded. Results: Among 7,710 de-duplicated records, 147 studies underwent full-text review, and 47 studies were included in quantitative synthesis, with reported adenoma detection for screening colonoscopy alone (n = 31), follow-up colonoscopy after a positive FIT alone (n = 4), follow-up colonoscopy after a positive mt-sDNA test alone (n = 4), and for more than one of the screening strategies of interest (n = 8). Across included studies, overall adenoma detection differed by screening pathway. Follow-up colonoscopy after a positive mt-sDNA test demonstrated the highest adenoma detection (66.3%; 95% CI, 61.2-71.1), with lower adenoma detection observed for colonoscopy after a positive FIT (50.6%; 95% CI, 43.4-57.8) and screening colonoscopy alone (33.8%; 95% CI, 30.9-36.8) (Table 1). Conclusions: Detection of adenomas was highest following colonoscopy performed after a positive mt-sDNA test compared with FIT-positive follow-up or screening colonoscopy alone. These findings highlight differences in downstream detection across CRC screening tests and suggest that, in settings where colonoscopy resources are constrained, initial mt-sDNA screening with timely follow-up colonoscopy may help prioritize patients most likely to benefit. CRC screening modality No. of Studies Adenoma detected Study population Proportion, % (95% CI) Heterogeneity, I² (%) Between-study variance (τ 2 ) P-value* mt-sDNA 8 17,436 29,098 66.3 (61.2-71.1) 94.6 0.0924 <0.0001 FIT 11 17,588 32,630 50.6 (43.4-57.8) 94.0 0.2187 <0.0001 Screening colonoscopy 38 2,351,801 6,378,891 33.8 (30.9-36.8) 99.8 0.1710 NA *P-value represents adenoma detection vs. screening colonoscopy adenoma detection.

e15060 Background: In metastatic Breast Cancer (mBC) Circulating Tumor Cells (CTCs) are an established prognostic indicator of patients (pts) with highly aggressive disease, poor clinical outcomes, and poor response rates to therapy. However, CTCs are typically found in < 20% of mBC pts and many pts without CTCs also progress. Cancer associated macrophage-like cells (CAMLs) are inflammatory tumor macrophages also found in blood, in > 90% of mBC, and are indicators of poor clinical outcomes independent of CTCs. We conducted a prospective study to model CTC & CAML subtypes from 212 mBC pt blood samples prior to induction of new systemic therapies to optimize and validate risk models based on 2-year outcomes of Progression-free survival (PFS) & Overall survival (OS). Methods: An observational multi-institutional prospective study was conducted on 212 mBC pts prior to induction of a new line of therapy who were progressing on their current therapy. Anonymized (7.5ml) whole blood samples were taken prior to therapy induction and filtered by CellSieve filtration. Quantities and subtypes of CTCs & CAMLs were categorized by their expression of CK+/CD45+/CD14+ for CAMLs and CK+/CD45-/CD14- for CTCs. PFS (RECIST v1.1) and OS hazard ratios (HRs) were calculated by censored univariate & multivariate analysis at 2 years. Results: Pt median age was 51 years (range 25-92); TNBC (44%), ER/PR+ (30%), HER2+ (15%). Pts were treated with chemotherapy alone (18%), immune checkpoint inhibitor (46%), targeted (40%), hormone (8%) and unknown (5%). 38% (81/212) pts had ≥1 CTCs which correlated with significantly poorer PFS (HR = 1.9; 95%CI 1.3-2.7; p = 0.0016) and OS (HR = 2.0; 95%CI, 1.3-3.0; p = 00025), with the most significant risk at ≥8 CTCs (14% pts), PFS (HR = 3.8; 95%CI, 2.1-6.9; p < 0.0001) and OS (HR = 7.2; 95% CI, 3.4-14.9; p < 0.0001). Independently, 93% (n = 196/212) of pts had ≥1 CAML, with a threshold of >40um size (84% pts) had significantly poorer PFS (HR = 2.0; 95% CI, 1.2-3.1; p = 0.0032), but not OS (HR = 1.5; 95%CI, 0.9-2.7; p = 0.1169). However, a threshold of >125um size CAML (43% pts) also had significantly poorer PFS (HR = 1.8; 95% CI, 1.2-2.7; p = 0.0013) and OS (HR = 1.6; 95% CI, 1.0-2.5; p = 0.0233). By combining models, the best outcomes were seen in pts with 0 CTCs & 0 CAMLs (mPFS = 12.6 & mOS = 21.3), followed by 0 CTCs & ≥40um CAMLs (mPFS = 5.2 & mOS = 17.5) and 0 CTCs & ≥125um CAMLs (mPFS = 4.9 & mOS = 15.2). Poorer outcomes were seen with ≥1 CTCs (mPFS = 3.3 & mOS = 13.5) and the worst outcomes with ≥8 CTCs (mPFS = 2.5 & mOS = 4.8). Conclusions: CTCs were uncommon in mBC pts but correlated with very poor clinical outcomes. In parallel analysis, CAMLs were common with CAML size correlating with increasingly poorer outcomes. By combining CTC & CAML subtypes, mBC pts were more accurately stratified by risk of progression and death. Additional multivariate studies correlating treatment class and tumor response rates are ongoing.

e14535 Background: Anti-programmed cell death ligand PD-L1/PD-1 immune checkpoint inhibitors (ICIs) are approved for metastatic breast cancer (mBC) patients (pts) with a tumor combined positive score (CPS) ≥10% in their tissue. However, many pts with < 10% CPS may also respond to ICIs. Recent studies in lung cancer have shown that circulating tumor cells (CTCs) and tumor-macrophage fusion cells (TMFCs) both express, and may upregulate, PD-L1 which is predictive for ICI responses. We initiated a prospective study to monitor PD-L1 in CTCs & TMFCs in mBC pts prior to receiving systemic ICIs to correlate their PD-L1 expression to progression free survival (PFS) and overall survival (OS) at 24 months. Methods: We conducted a multi-institutional prospective pilot study of n = 102 pts with pathologically confirmed mBC, having failed ≥1 prior lines of therapy, prior to receiving ICIs (n = 52 Pembrolizumab, n = 39 Retifanlimab, n = 5 Atezolizumab, and n = 1 Nivolumab). Anonymized blinded peripheral blood samples (7.5ml) were procured prior to ICI induction (T0) and (~40 days after ICI induction (T1). TMFCs & CTCs were isolated using Cellsieve microfilters with average PD-L1 expressions measured then categorized as negative/low or high. Tumor CPS was categorized as negative/low (< 10%) or high (> 10%). We compared TMFC PD-L1 to tissue CPS by linear regression. TMFC/CTC PD-L1 expression and tissue PD-L1 CPS were compared to pts’ PFS and OS by Cox proportional univariate and multivariate analysis over 24 months. Results: Of n = 102 pts, median age = 59 years (range 32-77); 42% (43/102) were ER+, 33% (33/102) were PR+, 5% (5/102) were HER2+, and 56% (57/102) were triple-negative. 32% (32/102) had an ECOG score of 0, 25% (26/102) had ECOG 1, and 43% of scores were unavailable. N = 42 pts had available tumor CPS data, which did not correlate to TMFC/CTC PD-L1 at T0 or T1. Pts with high CPS did not significantly predict for PFS (HR = 0.78; 95% CI, 0.3-1.9; P = 0.7627) nor OS (HR = 0.54; 95% CI, 0.2-1.7; P = 0.4471). Pts with high TMFC/CTC PD-L1 at T0 also did not significantly predict for PFS (HR = 0.74; 95% CI, 0.5-1.2; P = 0.2799) nor OS (HR = 0.84; 95% CI, 0.4-1.6; P = 0.7220). However, of the n = 82 pts who provided T1 samples, high CTC/TMFC PD-L1 at T1 was significant for better PFS (HR = 2.55; 95% CI, 1.6-4.2; P = 0.0004) and better OS (HR = 2.06; 95%CI, 1.1-3.8; P = 0.0309). Conclusions: In this study of mBC pts treated with PD-L1 ICIs, tissue CPS did not correlate with PD-L1 expression in CTCs or TMFCs. Further, neither CPS nor baseline PD-L1 in CTC/TMFCs predicted for clinical outcomes in ICI therapies. However, PD-L1 in CTC/TMFCs ~40 days post-induction of ICI did predict for better response rates. While this study suggests predictive value of monitoring PD-L1 in blood during ICI therapies, further studies are required to refine and validate these findings.

9524 Background: Unresectable melanoma in-transit metastases (ITM) can pose a significant clinical challenge. Our recently published data comparing first-line treatments for ITM, isolated limb infusion or perfusion (ILI/ILP), immune checkpoint inhibitors (ICI) and intralesional talimogene laherparepvec (TVEC), found superior outcomes with TVEC. However, TVEC was used more often in patients with lower disease burden and earlier stage (IIIB vs. IIIC/D). Therefore, we sought to better investigate these differences with a propensity score-matched (PSM) analysis. Methods: A multi-institutional, international IRB- approved retrospective analysis was conducted for unresectable melanoma ITM from 2016-2022. PSM analysis comparing first-line ILI/ILP, ICI, and TVEC for was performed. Patients were matched for stage, number of ITM, anatomical site, CLND status, gender and age. Kaplan-Meier curves (OS, PFS, DMFS) and Cumulative incidence function (MSS) were used to visualize time-to-event outcomes in the PSM cohort, though both methods do not account for the matched structure. Results: 274 patients were identified, 120 female/154 male; 96 treated with ILI/ILP, 111 with ICI, and 67 with TVEC. Median follow-up was 40 months (range, 1-80). PSM was performed and identified 36 TVEC–ICI pairs and 27 TVEC–ILI pairs. These were combined resulting in a final cohort of 108 observations (45 TVEC, 36 ICI and 27 ILI). The groups were well balanced. No statistical difference was found for metastasis-free survival (DMFS), progression-free survival (PFS), melanoma-specific survival (MSS), and overall survival (OS) between treatment modalities. TVEC was associated with significant improvement in local PFS (median was 2.2 years (y) for ILI/ILP, 1.5y for ICI and not reached for TVEC, p=0.048). While not statistically significant, a clinical benefit was seen in PFS being longer for TVEC (2.1y for TVEC vs. 1.2y for ILI/ILP and 1.1y for ICI; p=0.2) and OS (not reached vs 2.9y for ILI/ILP and 5.2y for ICI; p=0.2). On mixed effect Cox regression proportional hazard model using the matched data set, there were no significant differences in any of the survival and recurrence outcomes. Conclusions: When patients are propensity-matched, there were no significant differences in first-line treatment modalities for unresectable melanoma ITM. Treatment with TVEC did result in clinically meaningful improved overall and local PFS and OS. This supports that selection of ITM therapy should incorporate an individualized approach, incorporating disease distribution, stage, burden, treatment side effects and patient priorities.

8519 Background: Non-classical mutations (NCM) of epidermal growth factor receptor (EGFR) represent a broad group of oncogenic mutations in non-small cell lung cancer (NSCLC), often associated with resistance to osimertinib (e.g., P-loop and αC-helix compressing [PACC] mutations). Patients (pts) with NCM have inferior clinical outcomes with a high incidence of CNS metastases (CNSm). Silevertinib (BDTX-1535) is a fourth-generation, covalent EGFR TKI with high CNS penetrance targeting both EGFR classical mutations and NCM. The antitumor activity and safety of silevertinib in pts with advanced NSCLC were evaluated in a Phase 2 trial (NCT05256290). Methods: Pts with advanced EGFR NCM NSCLC who received no prior systemic therapy were enrolled (Cohort 3) based on a local molecular test. Silevertinib 200 mg was administered orally once daily. The primary endpoint of objective response rate (ORR) was assessed using RECIST v1.1. CNS ORR was assessed using Response Assessment in Neuro-Oncology for Brain Metastases (RANO-BM) in pts with no prior CNS therapy. Secondary endpoints include progression-free survival (PFS), duration of response (DOR), disease control rate (DCR), and safety. Results: From February 2024 to July 2025, 43 pts with 35 unique NCMs (including 25 pts with PACC mutations) were enrolled in Cohort 3: median age 70.0 years, 72% female, 74% white, and 42% never smoked cigarettes. As of November 3, 2025, median follow-up was 7.2 months. ORR by RECIST v1.1 is shown in the table. Sixteen pts (37%) had CNSm, including 7 pts (16%) with measurable CNS disease. RANO-BM CNS response was 86% (n=6/7). Complete clearance of EGFR VAF ctDNA was observed in 21/26 (81%) evaluable pts. Serious treatment-related adverse events (TRAEs) were reported in 5 pts (12%), and 4 pts (9%) discontinued treatment due to TRAEs. The most common TRAEs included rash (19%, grade 3), diarrhea (19%, grade 3), stomatitis (9%, grade 3), and paronychia (5%, grade 3). While 77% of pts had a dose reduction, 19/22 (86%) patients with a radiographic response maintained or deepened their response after dose reduction, including all patients with CNS response. Conclusions: Silevertinib demonstrated robust antitumor activity in treatment-naïve pts with a broad spectrum of NCM EGFR driver mutations with high intracranial activity in pts with brain metastases. The safety profile was consistent with the known AEs of the EGFR TKI class. Clinical trial information: NCT05256290 . Data as of November 3, 2025 N ORR n (%) 95% CI DCR n (%) 95% CI ITT Population * 43 26 (60) (44.4, 75.0) 39 (91) (77.9, 97.4) PACC mutations 25 14 (56) (34.9, 75.6) 22 (88) (68.8, 97.5) Compound mutations † 16 11 (69) (41.3, 89.0) 15 (94) (69.8, 99.8) *No pts with classical (E746_A750del or L858R) mutations were enrolled. † Presence of ≥ 2 NCMs. As of December 27, 2025, the 6-month PFS rate was 86% overall and 80% in pts with CNSm; available PFS and DOR data will be presented.

631 Background: Adolescent and young adult (AYA) women with breast cancer who have not completed their desired childbearing pre-diagnosis may be more likely to decline adjuvant endocrine therapy (ET) and/or to temporarily or permanently stop ET to pursue pregnancy. Fertility counseling and use of fertility preservation strategies (e.g., oocyte/embryo cryopreservation) might impact these decisions. Methods: In the Valuing Opinions and Insights from Cancer Experiences (VOICE) Study, we investigated whether use of fertility preservation strategies were associated with ET initiation and early discontinuation amongst AYAs with fertility concerns. Eligible females were diagnosed with stage 1–3 estrogen-receptor positive breast cancer at age 15-39 during 2013-2022 and responded to a survey in 2023-2024. Those who reported that they had not completed their desired family size or had been unsure about having completed their desired family size at the time of their cancer diagnosis were categorized as having had fertility concerns. ET initiation was defined as 2+ ET prescription fills within 18 months after diagnosis. Among ET initiators, we assessed early discontinuation (defined as lack of ET prescription fill over any 180 day period until 5 years after their first ET fill date). Due to inadequate power, we did not model the relationship between oocyte/embryo cryopreservation and ET initiation. However, we did have power to assess the association between oocyte/embryo cryopreservation and ET discontinuation using multivariable Cox regression to calculate Hazard Ratios (HR) and 95% Confidence Intervals (CI). HRs for discontinuation were adjusted for age at diagnosis, stage, study site, diagnosis year, income, and children before diagnosis (yes/no). Results: Among 518 AYA breast cancer survivors, 56% (N = 290) had fertility concerns at diagnosis. Of these 290, 41% had 1+ child before diagnosis, 90% received fertility counseling, 27% froze eggs or embryos, and 10% had 1+ child after diagnosis. The majority (89%) initiated ET. Among the 32 who did not initiate ET, 7 (22%) reported that fertility concerns impacted that decision. Oocyte/embryo cryopreservation was used by 26% of ET initiators and 34% of ET non-initiators. Among the 258 ET initiators, 89 (35%) discontinued ET early. Compared to those who did not use fertility preservation strategies, patients who froze oocytes/embryos were more likely to discontinue ET (HR 1.89; 95% CI 1.18–3.05). Among those who discontinued ET, 19% had 1+ child after diagnosis (compared to 2% among those who did not discontinue ET). Conclusions: This study confirmed prior studies showing that many AYAs with breast cancer have fertility concerns, and these concerns may impact decisions about ET. In our analysis, those who cryopreserved oocytes/embryos were more likely to discontinue ET early, and a higher proportion who discontinued ET had 1+ live birth after breast cancer.

635 Background: Prospective data on efficacy, quality of life, and treatment-related toxicities in older adults with breast cancer are limited. The ATOP trial (NCT03587740) evaluated T-DM1 in older adults and demonstrated favorable 5-year invasive disease-free survival. Here, we report patient-reported adverse events (AEs) and health-related quality of life (HRQOL) findings from ATOP. Methods: ATOP was a single-arm, phase II, multicenter study of adjuvant T-DM1 for those aged 60 with stage I-III HER2+ breast cancer. Protocol therapy included postoperative administration of T-DM1 (3.6 mg/kg) every 21 days for one year (17 cycles). PRO-CTCAE (assessing specific symptoms) and EQ-5D (a measure of HRQOL) surveys were administered electronically or on paper at baseline (pre-treatment), on Day 1 of each treatment cycle, and at a single 6–12-month post-treatment time point. Participants who responded to the baseline and at least one follow-up survey were included in the PRO analysis. EQ-5D changes from baseline were assessed using general linear mixed models. Summary statistics were used to assess PRO-CTCAE scores to evaluate which symptoms developed between baseline and 1 subsequent survey(s) and their severity. Results: Among the 111 patients enrolled on ATOP (median age=71, range 60-88 years), 98 responded to the baseline survey and 1 subsequent survey(s). 1435 surveys were returned that included at least one PRO-CTCAE response, and 1661 surveys were returned that included EQ-5D. The Table displays the % of participants who reported PRO-CTCAE symptoms that worsened from baseline to any severity level (scores >0) or to a severe level (scores ≥3). More than 60% of survey respondents reported new or increased dry mouth, fatigue, muscle aches, decreased appetite, nausea, pain, and/or numbness/tingling at some point during or after treatment, but these were usually not severe. EQ-5D scores did not change significantly from baseline at any time point. Conclusions: In this adjuvant trial for patients aged >60, participation rates for PRO data collection were high. Reassuringly, global HRQOL was not impacted by T-DM1, and though frequently reported, the vast majority of patient-reported symptoms were mild. Future analyses of this trial will focus on duration and predictors (clinical and biomarker-based) of severe AEs, agreement between patient-reported and clinician-reported AEs, and whether sharing PRO reports with clinicians impacted clinician-reported AE grades. Clinical trial information: NCT03587740 . Most common new or worsening symptoms reported via PRO-CTCAE in ATOP (n=95). Symptom % with score >0 n (%) with score 3+ Dry mouth 79% 26% Fatigue 71% 29% Muscle aches 69% 20% Decreased appetite 69% 12% Nausea 67% 6% Pain 66% 21% Numbness/tingling 65% 9% Blurry vision 60% 4% Mouth or throat sores 60% 5%