Wiedmeier, Julia E.

ABSTRACT Ciltacabtagene autoleucel (cilta‐cel) has demonstrated excellent efficacy and long‐term disease control in patients with relapsed/refractory multiple myeloma (RRMM). However, a proportion of patients experience early treatment failures. We investigated clinical factors associated with early progression or death (within 12 months) in patients with RRMM receiving standard‐of‐care cilta‐cel across the three Mayo clinic centers. Patients with a follow‐up of at least 12 months or progression or death within 12 months from infusion were included. Of the patients with early treatment failure ( n = 52), 69% had progressive disease and 31% had a non‐relapse mortality (NRM) event. In patients without early treatment failure ( n = 164), 13% of events were NRM. Among pretreatment factors, prior BCMA‐directed therapy, presence of extramedullary disease and a CAR‐HEMATOTOX score of ≥ 2 were independent predictors of early progression or death. The utilization of cilta‐cel in earlier lines of treatment (1–3 vs. 4 or more) demonstrated comparable PFS (12‐month PFS 73% vs. 77%, p = 0.94). Measurable residual disease positivity in the bone marrow at 3 months (11/197 patients) identified a small but high‐risk group with an increased risk of early treatment failure (OR 5.68; p = 0.012). Patients with less than a complete response on a FDG PET/CT at 3 months also had an increased risk of early treatment failure (OR 11.8; p < 0.0001). Our findings may help identify patients at high‐risk for early adverse outcomes despite receiving highly effective therapy, and support consideration of novel therapeutic strategies within a clinical trial setting.

ABSTRACT Background A randomized phase II screening trial of gemcitabine, nab‐paclitaxel, and cisplatin with a medically supervised ketogenic diet (MSKD) versus usual diet (non‐MSKD) was conducted in patients with treatment‐naive metastatic pancreatic ductal adenocarcinoma (PDAC). Methods Patients with untreated metastatic PDAC were randomized 1:1 to MSKD or non‐MSKD while receiving gemcitabine, nab‐paclitaxel, and cisplatin on days 1 and 8 of a 21‐day cycle. The MSKD was guided by a remote health care team and daily ketone (beta‐hydroxybutyrate) levels, with goal beta‐hydroxybutyrate of 0.5 to 3.0 mM. The primary endpoint was progression‐free survival (PFS) using a one‐sided alpha level of 0.20. Secondary endpoints included overall survival (OS), safety, and quality of life (QOL). Changes in microbiome were an exploratory endpoint. Findings Overall, there were 32 evaluable patients. In the MSKD arm, 15 of 16 patients achieved nutritional ketosis; the median proportion of days in ketosis was 39.4%. The median PFS was 8.5 months in MSKD patients and 6.2 months in non‐MSKD patients: hazard ratio, 0.53 (95% CI, 0.21–1.37); one‐sided p = .096. The median OS was 13.7 months with MSKD and 10.2 months in the non‐MSKD arm: hazard ratio, 0.58 (95% CI, 0.25–1.37); one‐sided p = .107). All MSKD‐related adverse events were grade 1‐2. There were no significant differences in grade ≥3 chemotherapy‐related adverse events between the arms. MSKD patients had no decline in QOL and had significant enrichment of beneficial taxa in the microbiome ( p < .05, log‐fold change ≥2). Conclusions The MSKD is feasible in patients with PDAC and, although not powered for definitive outcomes, shows trends in improved PFS and OS when combined with gemcitabine, nab‐paclitaxel, and cisplatin, without added toxicity or detriment to QOL. Larger studies are required to confirm these findings and establish the value of the MSKD in pancreatic cancer treatment.

Abstract Multiple myeloma (MM) with t(11;14)(CCND1;IGH) remains the only subset sensitive to the BCL2 inhibitor venetoclax. However, not all patients with t(11;14)(CCND1;IGH) respond to treatment, and some progress early after initial response. To investigate this, we examined 44 whole-genome and whole-exome sequencing data samples from 34 patients with t(11;14) MM treated with venetoclax. The presence of mutations in the RAS pathway was strongly associated with shortened progression-free survival (PFS) and was validated in an independent cohort of 21 patients with MM. The presence of 1q gain was also associated with shorter PFS in patients without RAS mutations. In 10 patients with paired prevenetoclax and postvenetoclax treatment samples, postvenetoclax progression was recurrently driven by the selection of genomic events in the BCL2/MCL1 and RAS pathways and of high-risk features (eg, loss of TP53 and CDKN2C). Overall, our study shows that comprehensive genomic profiling can identify most mechanisms underlying resistance to BCL2 inhibition in t(11;14)(CCND1;IGH) MM.

Abstract Background: Minimal residual disease (MRD) is a critical prognostic and therapeutic response marker in multiple myeloma (MM). Two main technologies are used for MRD assessment in bone marrow: next-generation flow cytometry (NGF) and next-generation sequencing (NGS), from clonoSEQ. While both methods are FDA-cleared and clinically relevant, they differ in sensitivity, sample handling requirements, and technical differences. Comparative performance in real-world matched samples is understudied. Here we compared the detection rates and concordance between MRD by NGF (flow cytometry) and NGS-based clonoSEQ, using paired bone marrow aspirates collected at the same clinical timepoint. Methods We identified 246 paired bone marrow samples from MM patients, which were evaluated by both flow cytometry (Euroflow, typically sensitivity of 10-5) and clonoSEQ (sensitivity of up to 10-6) on the same collection date.MRD-negativity for clonoSEQ was defined as no detectable clones and below the assay's level of detection (LoD). Continuous variables (clonoSEQ and flow CPS) were analyzed using the Mann-Whitney U test. Categorical variables were assessed using chi-square tests with Yates continuity correction for 2x2. A cox proportional hazards model was used to evaluate the association between overall survival and cytogenetic abnormalities, MRD status, and other clinical covariates including age, sex, treatment type, and disease setting (newly diagnosed, relapsed/refractory). A p-value &lt; 0.05 was considered significant. Results Out of 246 paired bone marrow samples, we identified 173 concordant samples, out of which 26 were concordant positive (clonoSEQ+/NGF+), 147 were concordant negative (clonoSEQ-/NGF-), and 73 were discordant (clonoSEQ+/NGF-). clonoSEQ detected MRD in all cases missed by NGF, including some with relatively high tumor burden, reflecting its higher sensitivity. Among discordant samples, 45 (61.6%) were following treatment of newly diagnosed MM (NDMM) and 28 (38.4%) treatment of relapsed/refractory (RRMM). Among the MRD-positive samples, the concordant group (n=26) showed a mean clonoSEQ count of 11923.5 cells per million (CPM) and a mean NGF CPM of 305.5 (p&lt;0.01). In contrast, the 73 discordant samples had a lower mean clonoSEQ CPM of 156.1. For the 147 MRD-negative samples with concordant results, no residual disease was detected by either assay (CPM = 0 for both). When evaluating sex, race, ethnicity, chromosomal abnormalities, prior treatments to sample collection (immunomodulatory drugs, proteasome inhibitors, CD38 antibodies, CAR Ts/bispecific antibodies), and disease stage (NDMM, RRMM, untreated), patients with t(11;14) were significantly higher in the discordant group (17.9% concordant vs. 32.9% discordant; p = 0.016), while CAR T/bispecific antibody-treated patients were more likely concordant for the tests (27.2% concordant vs. 4.1% discordant; p&lt;0.01). High-risk cytogenetics (t(4;14), t(14;16), gain 1q) were associated with worse survival (HR 6.22, 95% CI 2.02 – 19.2; HR 16.2, 95% CI 3.38-77.1; HR 4.0, 95% CI 1.28 – 12.5, respectively). Discordant MRD status did not impact survival, though only 13/246 patients were deceased (median follow-up approximately 50.6 months).Conclusion: ClonoSEQ demonstrates higher sensitivity compared to NGF for MRD detection in MM, identifying residual disease missed by NGF particularly in t(11;14) cases. Discordance did not affect survival, however, only 13 patients were deceased at the time of last follow up, suggesting longer follow up is needed.

Abstract Background: The phase II and III GRIFFIN and PERSEUS studies evaluated DVRd vs. VRd in NDMM pts that were transplant eligible (TE). These studies included consolidation (cons) and dual agent maintenance (maint) with dara and len (DR). Little is known about the efficacy of DVRd in RW practice including frequency of bor use, use of cons, use of DR maint, and subsequent treatment after progression (PD) on DVRd. We aim to evaluate the RW efficacy of NDMM pts treated with DVRd across the tri-site Mayo Clinic Comprehensive Cancer (MCCC). Methods: We retrospectively analyzed the medical records of pts treated with DVRd between June 2018 and June 2024 at the MCCC. Outcomes were estimated using the Kaplan-Meier method. Results: 464 pts were included; 278 pts were male, and the median (m) age of MM diagnosis was 64 years (yr). 114 pts had ISS III, 205 pts had R-ISS III, 266 pts had high risk (HR) FISH, 80 pts had extramedullary disease, 165 pts had ultra HR disease (dz) (as per 2025 IMS/IMWG consensus), and 47 pts had renal insufficiency (RI) with creatinine &gt;2 mg/dL. Starting len dose was 25mg in 356 pts, 15 mg in 40 pts and ≤10mg in 65 pts. 399 pts received bor 1x per week and 63 2x per week, 91 pts received 1-2 cycles of a different regimen prior to DVRd due to hospitalization (n=23), RI (n=38), poor performance status (n=6), other (n=34). 315 (67.9%) pts underwent autologous transplant (ASCT). The m number of induction cycles was 5; 4 for pts who underwent ASCT and 6 for pts who did not. The best ORR to induction for pts who underwent ASCT was 98% with 247 (79%) achieving ≥VGPR, and 82 (26%) achieving minimal residual disease negativity (MRD-) to at least 10-5. The best ORR for pts who did not undergo ASCT was 87%. For those who underwent ASCT, (96% with melphalan 200mg/m2), the ORR at day 100 was 97% with 56% achieving MRD-. At 1-yr post ASCT, 30% (93/312) were MRD-. 42 pts (13%) received post ASCT cons with DVRd for a m of 2 cycles. 281 pts received post ASCT maint including 107 (38%) len, 53 (19%) bor-len, 91 (32%) dara-len, 14 (5%) dara, 16 (6%) other. 61(13%) pts had change in treatment, due to change to second line therapy (35; 55%), discontinuation (d/c) of len (11; 17%), d/c of dara (3; 5%), d/c of bor (15; 23%), d/c of dex (0; 0%). The m follow-up time for all pts was 26 months (mo) (17-39). The m PFS of pts who underwent ASCT was not reached (NR), and was 57 mo (52-NA) for pts who did not undergo ASCT. For pts who underwent ASCT, the PFS at 24mo for pts who did not have HR FISH was 93% (88-99%) compared to 80% (73-88%) for pts with HR FISH (p=0.12) and 77% (68-87%) for pts with ultra-HR dz (p=0.013).The PFS at 24mo of pts with RI who underwent ASCT was 81% (66-98%) compared to 86% (82-92%) for those without RI, p=0.57. The PFS at 24mo of pts with RI who did not undergo ASCT was 53% (28-100%) compared to 64% (55-75%) for those without RI, p=0.42. The ORR and MRD- rate for pts who received once-weekly bor was 94% and 24%, compared to 94% and 27% for pts who received 2x weekly bor (p=0.85, p=0.93). For pts who underwent ASCT, the PFS at 24mo for pts who received len maint was 91% vs. 83% for pts who receive dual agent maint (DR or VR) (p=0.25), although pts who got dual agent maint were more likely to have HR FISH than pts who received len maint (p&lt;0.001). The PFS at 24mo for pts that received post-ASCT cons was 91% compared to 85% for those that did not (p=0.53); pts who got post-ASCT cons were more likely to have HR FISH (p=0.07). For pts that underwent ASCT, the 3 yr PFS rate is 85% and the 3 yrs OS rate is 96%. For pts that did not undergo ASCT the 3 yrs PFS rate is 60% and the 3 yr OS rate is 85%. 55 pts had functional HR (FHR) MM (relapse within 18 mo) and m PFS for FHR pts who underwent ASCT was 15 mo (11-NA), while m PFS was NR for pts without FHR MM (p&lt;0.001). 79 pts relapsed after 1st line DVRd. The most common 2nd line therapies (tx) were dara-carfilzomib (K)-D, dara-pomalidomide(P)-D, KPD, and other. The m follow-up time from 2nd line tx was 10 mo, the best ORR to 2nd line tx was 76%, and the m PFS with 2nd line tx was 18 mo (7-NA). Conclusion: In this RW analysis, the efficacy and survival outcomes of NDMM pts treated with DVRd was comparable to that reported in the PERSEUS and GRIFFIN trials, although MRD- rates appear lower. DR maint and post-ASCT cons use was not common and was used more frequently in pts with HR FISH. Pts can be effectively salvaged following PD on front-line DVRd with available tx.

Abstract Background The advent of T-cell redirecting bispecific antibodies (BsAb) therapies has led to deeper and durable responses in patients with RRMM. We sought to identify adverse prognostic factors for patients treated with BsAbs. We also explored whether the extent of the non-involved free light chain (niFLC) suppression could serve as a potential marker of T-cell engager activity, given the binding of BsAbs to both clonal and non-clonal plasma cells and the short half-life of serum FLCs. Methods We conducted a retrospective analysis of RRMM patients treated with BsAbs between 2022 and 2025 at Mayo Clinic. Baseline lymphocyte counts and ferritin levels were collected and analyzed both as continuous and dichotomized variables. niFLC was considered undetectable if it was below the quantification limit, while the magnitude of niFLC suppression was defined as the absolute difference between niFLC levels and the lower normal range threshold at the time of best response. In addition to standard statistical methods, interaction models were used to explore the potential effect modification of niFLC dynamics. Results A total of 158 patients were included (teclistamab, 73%; talquetamab, 15%; elranatamab, 12%). The median follow-up is 12 months (range 0 to 28 months). Median age is 71(range 65 to 77); 52% (n=85) were triple-class refractory (refractory to an IMiD, a PI, and CD38-antibody) and 37% (n=60) were penta-refractory. CAR-T therapy was previously administered in 28% (n = 46) patients, and 70% had undergone an autologous stem cell transplant. One or more high risk cytogenetic features including del(17p), gain(1q), amp(1q), del(1p), t(4;14), and t(14;16) were present in 57% (n = 90) of patients. Extramedullary disease was noted at the time of BsAb therapy in 44% of patients. Utilizing IMWG response criteria, 68% (n=107) achieved ≥partial response, and 64% (n=101) had ≥ very good partial response (VGPR) as best response following BsAb treatment. The median time to best response was 1.6 months (range 0.7 to 4.4). On multivariable analyses, baseline immunoparesis (HR 1.96; 95% CI, 1.08–3.58; p = 0.0274) and elevated ferritin levels (≥ 337 ng/mL) (HR 1.96; 95% CI, 1.24–3.09; p = 0.0041) were independent predictors of inferior progression-free survival (PFS). Lower baseline absolute lymphocyte count, analyzed as a continuous variable, was significantly associated with shorter PFS in the univariable analysis (HR 0.66; 95% CI, 0.44–0.98; p = 0.04), but not in the multivariable model (HR 0.75; 95% CI, 0.5–1.13; p = 0.166). Detectable niFLC at the time of best response was also significantly associated with inferior PFS (HR 1.80; 95% CI, 1.14–2.84; p = 0.0114). However, the magnitude of niFLC suppression did not show a statistically significant impact on PFS. The median PFS was 5 months in patients with high ferritin levels (≥ 337 ng/mL) and 21 months in those with lower ferritin (p = &lt; 0.005). Similarly, PFS was 8 months in those with immunoparesis and not reached in those without baseline immunoparesis (p = 0.008). At the time of best response, detectable niFLC was associated with a trend toward shorter PFS (5 vs. 13 months), although the difference was not significant (p = 0.06). Logistic regression analysis supported these findings, with higher ferritin levels (OR 2.28; 95% CI: 1.09–4.96; p = 0.032) and the presence of baseline immunoparesis (OR 2.60; 95% CI: 1.18–6; p = 0.02) being significantly associated with higher likelihood of progression or death. Patients with deep reduction in niFLC achieved a VGPR or better. In contrast, those with detectable or higher-than-normal niFLC levels did worse in terms of response. Notably, niFLC became undetectable in 72% of patients with ≥VGPR (73/101), compared to 52% of those who did not achieve this level of response (30/57). Conclusion Among RRMM patients treated with BsAbs, baseline immunoparesis and elevated ferritin levels emerged as independent predictors of worse PFS. While failure to induce a deep reduction in niFLC at the time of best response suggests a tumor extrinsic mechanism of resistance, and it is also linked to inferior outcomes.

Abstract Introduction Matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS, mass fix) represents a sensitive and specific alternative to electrophoresis and immunofixation for quantifying monoclonal antibodies in patients with multiple myeloma (MM). Here we report real world data utilizing mass fix and compare its test characteristics to a gold standard of minimal residual disease (MRD) quantification utilizing next generation sequencing (NGS). Results All patients who had obtained mass fix and MRD testing by NGS as part of routine clinical care at Mayo Clinic Arizona were screened for this study. In total, 343 pairs of mass fix and NGS testing within 50 days of each other representing 269 unique patients with secretory multiple myeloma were included. Cases of IgD myeloma and those secreting only free light chains were excluded. The threshold of MRD negativity was set at &lt;1x10-6(less than one malignant cell in one million) and was assessed utilizing the clonoSEQ NGS assay. The median age of our cohort is 67, it is 44% female, and primarily Caucasian (88%) with a median follow-up of 7.3 months from testing date. FISH testing was performed in 96% of patients and at least one high risk cytogenetic abnormality (t(4;14), t(14;16), del(17p)) was found in 23% of patients. The t(11;14) translocation was found in 18%, +1q in 26%, and amp(1q) in 6% of evaluated patients. Notably, patients at all stages of treatment or disease status were included in our study. Induction treatment for newly diagnosed MM (NDMM, 133 patients) was mostly daratumumab-containing quadruplet (63%) or triplet drug regimens (36%). Autologous stem cell transplant (ASCT) was performed in 79% of NDMM and 80% of relapsed refractory MM patients (RRMM, 138 patients). Of the RRMM patients, 94% were triple class exposed and 41% were penta-exposed. Overall agreement between NGS and mass fix results was 65% (Kappa statistic: 0.31, 95% CI: 0.22 – 0.41). Most discordant cases were instances of mass fix negativity and NGS positivity (n = 89, 26% of all testing pairs). Only 7% of cases (n= 30) represented mass fix positivity with NGS negativity. Mass fix was able to define therapeutic monoclonal antibody by its unique mass spectrometric profile in 38 of the total test pairs that otherwise would have been considered disease associated. Of the 30 patients testing mass fix positive and NGS negative, 25 (83%) represent post-treatment evaluations. Thus, ongoing mass fix positivity represents monoclonal protein washout kinetics. All of these cases are noted to have declining mass fix levels at last follow up and 40% had undetectable monoclonal protein. The discordant mass fix negative and NGS positive cases were evenly distributed across NDMM and RRMM representing 32% and 20% of test pairs in each group, respectively. Amongst these 89 total test pairs, the median abundance of malignant clone by NGS was 10 cells per million (range 0.06 to 297,895). This is in contrast to 136 concordantly positive test pairs where the median was 2960 cells per million (range 0.353 to 1,017,360). The median monoclonal protein identified (in those with a quantifiable M-spike) was 0.30 g/dL. Receiver operating characteristic curves using NGS as gold standard found the optimal mass fix threshold to be 0.010g/dL (specificity 95%, sensitivity 51%) for NDMM patients and 0.046g/dL (specificity 84%, sensitivity 55%) in RRMM patients. Conclusions Development of a MRD assay based on peripheral blood sampling could greatly improve the ease and speed of obtaining these assessments. Our experience highlights both the great potential and need to identify appropriate clinical contexts for optimal use of mass fix MRD assessment. A significant limitation of our data is that low level monoclonal proteins without a previous reference above a threshold of 20mg/dL are not reported as positive and may account for a significant fraction of discordant cases reported here. All clonoSEQ NGS samples are referenced to a positive control greatly increasing specificity. The currently reported dataset is biased against mass fix as not all test pairs reported are known to have a positive reference. Further delineation of these cases is forthcoming. Previous reports have also noted that mass fix test characteristics can improve with time from treatment which will be assessed with future follow-up.

Abstract Introduction Cila-cel is associated with a 10-15% risk of delayed neurotoxicity (DNT) with rates of cranial nerve palsies (IEC-NP) and parkinsonism (IEC-PKS) seen at a rate of 10% and 1-4% respectively and can occur as early as 3-4 weeks after infusion. We and others have shown that high post-infusion peak absolute lymphocyte count (ALCpeak) of &gt;3x10^9/L is associated with an increased risk of delayed neurotoxicity (Lim et al., ASCO 2025) whilst the risk was negligible (~1%) when ALCpeak fell below that threshold. Since December 2024, we implemented prophylactic administration of dexamethasone (PPX DEX) when ALC was &gt;3x10^9/L (defined as high ALCpeak). Outcome of these patients are described here. Methods Analysis of clinical outcome included 230 pts treated between Feb 2022 and Nov 2024 as a historical cohort and 102 patients treated between Dec 2024 and May 2025 after the introduction of dexamethasone prophylaxis using an oral dose of 10mg twice a day for at least three days in the high ALCpeak cohort. Results No significant differences were seen between the new and historical cohort in pre-lymphodepletion disease burden (bone marrow plasma cell %, involved light chain or M-spike level), and rates of all/high-grade CRS or ICANS, IEC-HS and rates of tocilizumub use. Median follow-up in the new cohort of 102 pts was 3.6 months (95% CI 3.3-4.2). Eleven (10.8%) developed DNT [3 (2.9%) with IEC-PKS, 8 (7.8%) with IEC-NP]. High ALCpeak of &gt;3x10^9/L was observed in 51 (50%) pts. Among pts with high ALCpeak, DNT was observed in 10 (20%) pts [3 (5.9%) with IEC-PKS, 7 (13.7%) with IEC-NP] whereas among 51 pts with ALCpeak &lt;3x10^9/L, DNT was observed in 1 (2%) pt [1 (2%) with IEC-NP]. In the high ALCpeak cohort, 38 (75%) received DEX [6 (12%) for toxicity management, 32 (63%) PPX DEX]. Of the 38 pts treated with DEX, DNT was observed in 6 (16%) pts (2 (5.3%) IEC-PKS, 4 (10.5%) IEC-CNP). We next compared DNT rates between this new cohort of high ALCpeak pts receiving DEX (n=38) against the historical cohort with high ALCpeak (n=98). Estimated 90-day DNT by Kaplan-Meier method was (19.2% vs 20.5%; p=0.53): IEC-PKS (5.8% vs 7.2%; p=0.60) and IEC-NP (11.7% vs 13.3%; p=0.58). In patients with high ALCpeak, the use of DEX did not appear to significantly reduce the risk of DNT compared to historical controls (HR 0.76, 0.33-1.78), IEC-PKS (HR 0.67, 0.14-3.10) or IEC-NP (0.73, 0.24-2.23). We next compared ALC expansion over the first month post CAR-T infusion (area under the curve, AUC). Among the new cohort of 102 patients, no difference was seen in the AUC of pts who received DEX but did not develop DNT vs those who developed DNT (31.0 vs 57.9, p=0.28); No difference in AUC was seen in the new high ALCpeak cohort receiving DEX vs the historical cohort with high ALCpeak (36.0 vs 43.8, p=0.15) Of the eight cases of IEC-NP, 4 received PPX DEX. No noticeable differences were observed in the severity of presentation, laterality of cranial nerve involvement and rates of multiple cranial nerve involvement between these 4 cases who received PPX DEX and the 16 cases from the historical cohort. At the time of database freeze, 3 of the 4 cases had resolved and 1 was improving. Median time to complete symptom resolution was 38 days vs 69 days in the historical cohort. Of the three cases of IEC-PKS, 2 received PPX DEX. Median time to symptom onset for IEC-PKS was 46 days (vs. 24 days in historical cohort). Both cases had severe symptoms non-responsive to first line high-dose methylprednisolone, second line intrathecal chemotherapy and third line high-dose cyclophosphamide. Both pts subsequently died from sepsis 28 and 67 days post-cyclophosphamide. Conclusion While ALCpeak &gt;3x10^9/L predicts risk of DNT in pts treated with cilta-cel, the use of PPX DEX does not appear to significantly reduce ALC expansion and does not appear to significantly reduce the risk of DNT, IEC-PKS or IEC-NP. Other strategies to reduce ALC or alter T cell functions may need to be considered.

Abstract Introduction: Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease with limited treatment options and poor survival. This study explores how a medically supervised ketogenic diet (MSKD) impacts the gut microbiome and treatment response in patients with newly diagnosed metastatic PDAC receiving gemcitabine, nab-paclitaxel, and cisplatin chemotherapy. Methods: As part of a randomized Phase II trial, 32 evaluable patients (median age 65.9 years; 53% male), 16 were randomized to either MSKD or standard diet (SD) combined with chemotherapy. Stool samples were collected from 4 patients in the MSKD group (13 samples) and 8 patients in the SD group (23 samples). Deep shotgun metagenomic sequencing was conducted using NovaSeq (Illumina). Taxonomical and functional microbiome characterization was performed using MetaPhlAn 4.0 and HUMAnN 3.6 (The Huttenhower Lab, Harvard). Comprehensive bioinformatics analyses, using QIIME2, were performed to analyze microbiome composition and function over time. Results: Patients in the MSKD group showed better treatment responses overall. Microbiome profiles between the two groups remained distinct throughout therapy. Though not statistically significant due to sample size, MSKD patients showed lower alpha diversity (Shannon diversity; p-value=0.1339), likely reflecting reduced intake of fermentable fiber. Differential abundance analysis using the ANCOM-BC method revealed a significant enrichment of beneficial taxa in the MSKD group compared to the SD group (p&lt;0.05, log-fold change [lfc]≥2), including Akkermansia muciniphila (linked to improved response to immune checkpoint inhibitors; p=0.017931, q=1), Intestinimonas butyriciproducens (a short-chain fatty acid [SCFA] and butyrate producer; p=3.09E-05, q=0.017), and Streptococcus thermophilus (a supporter of gut mucosal health; p=1.15E-05, q=0.006). During the course of the study, only MSKD patients showed sustained increases in Roseburia hominis (SFCA/butyrate producer; p=3.94E-05, q=0.021) and Lacticaseibacillus rhamnosus (with anti-inflammatory and immune-modulating properties; p=7.28E-19, q=3.98E-16), along with a marked reduction in potentially pro-inflammatory Actinomyces spp.(p≤4.47E-05, q≤0.024). Functional profiling showed increased abundance of cancer-relevant microbial pathways in MSKD patients, including phosphatidate metabolism (PWY-7039; involved in lipid signaling and immune regulation; p=4.36E-04, q=0.20) and allantoin degradation (PWY-5705; linked to redox balance; p=9.16E-06, q=0.004). Conversely, L-ascorbate biosynthesis V (PWY-6415) was reduced (p=3.80E-04, q=0.17), likely due to decreased D-galacturonate substrate availability from fiber restriction. Conclusion: These findings suggest that an MSKD may beneficially modulate the gut microbiome in ways that support and enhance therapeutic response in patients with PDAC. Further validation in a larger cohort is warranted to confirm these results and improve analytical resolution. Citation Format: Keehoon Lee, Derek Cridebring, Gayle S. Jameson, Denis J. Roe, Erkut Borazanci, Diana L. Hanna, Caroline G.P. Roberts, Meredith S. Pelster, Richard C. Frank, Angela T. Alistar, Alan M. Miller, J. Erin Wiedmeier-Nutor, Sandra D. Algaze, Alison R. Zoller, Sarah J. Hallberg, Betsy C. Wertheim, Joshua D. Rabinowitz, Stephen Gately, Jennifer Keppler, Sunil Sharma, Drew W. Rasco, Daniel D. Von Hoff. Ketogenic Diet Modulates Gut Microbiome Composition and Enhances Treatment Response in Patients with Advanced Pancreatic Cancer: A Phase II Study [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research—Emerging Science Driving Transformative Solutions; Boston, MA; 2025 Sep 28-Oct 1; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85(18_Suppl_3):Abstract nr B094.