Abstract Peritoneal Carcinomatosis (PC) is a metastatic cancer of the lining of the abdominal cavity, most often originating from the gastrointestinal or gynecological tracts. PC occurs in approximately 20% of colorectal cancer and 60% of ovarian cancer cases, with estimated 5-year survival rates as low as 6%. Pressurized intraperitoneal aerosolized chemotherapy (PIPAC) is a locoregional drug delivery modality administered via a minimally invasive laparoscopic approach. PIPAC shows promise in the treatment of peritoneal metastasis in early trials on colorectal cancer (CRC) or appendiceal cancer (AC) in patients who cannot undergo cytoreductive surgery. The spatial organization of the tumor microenvironment (TME) and the complex cellular interactions within profoundly shape biology and treatment response. Spatial transcriptomics offers an opportunity to characterize TME heterogeneity in its native architecture, allowing the identification of biomarkers, interactions, and gene expression programs as well as resistance mechanisms and new potential targets. We performed image-based spatial transcriptomic profiling of 152 tissue samples, including 50 pre-treatment and 65 post-treatment metastatic tumors and 17 pre-treatment and 20 post-treatment tumor-adjacent normal tissue samples from 19 patients who participated in a Phase I trial on Oxaliplatin PIPAC. Through a comprehensive characterization of transcriptional profiles of a total of 1,249,711 cells, as well as cellular neighborhood and ligand-receptor interactions, we describe the heterogeneity of PC in its spatial context. We have further characterized treatment-driven changes in pre- and post-treatment tumors of a subset of 7 patients who underwent PIPAC with mitomycin IP. Through cell-based niche and proximity analyses, we identify distinct shifts in the composition and architecture of treated tumors. Most notably, treatment resulted in an 87% decrease in the number of malignant cells, as well as an expansion of the plasma-barrier niche and an increased number of immune infiltrates. Further analysis revealed distinct differences in the abundance of specific cancer-associated fibroblast and immune subsets, demonstrating changes in TME architecture. Overall, our results provide an invaluable characterization of PC in CRC and AC, garnering new insight into their architecture, cellular composition, and cell-cell interactions at baseline and in response to regional chemotherapy. Further analyses and follow-up studies can identify and validate new, actionable biomarkers to target these hard-to-treat tumors. Citation Format: Heini Maaret Natri, Arianna L. Williams-Katek, Muhammad Talha Waheed, Tiana Li, Marwan Fakih, Mingye Feng, Amit Merchea, Sue Chang, Richard L. Whelan, Danielle Deperalta, Thanh H. Dellinger, Nicholas Banovich, Mustafa Raoof. Spatial transcriptomic profiling of peritoneal metastases identifies multicellular programs in patient tumors undergoing pressurized intraperitoneal aerosol chemotherapy (PIPAC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3958.

INTRODUCTION:Advances in robotic instrumentation have facilitated minimally invasive completion of complex cancer operations. The objective of this study is to determine the feasibility of robotic approach for cytoreduction (R-CRS) for peritoneal carcinomatosis in a series of 16 consecutive cases. METHODS:Single institution retrospective study of consecutive patients with peritoneal carcinomatosis deemed appropriate for R-CRS after multidisciplinary review between 2017 and 2022. Feasibility was defined as the proportion of patients in whom complete cytoreduction was achieved without conversion to open. RESULTS:A total of 16 patients (median interquartile range [IQR]: age 60 ys [45.8-70.5], body mass index 29 [24.5-33.6], peritoneal carcinomatosis index 5 [2.8-6.3]) underwent R-CRS of which six also received hyperthermic intraperitoneal chemtotherapy. Seven patients had gastrointestinal primary cancers (3 colorectal, 3 appendiceal, 1 small bowel neuroendocrine); and nine had gynecologic cancers (7 ovarian, 2 endometrial). Median operative time was 6.0 h (IQR: 5.0-9.0), and median estimated blood loss was 87.5 mL (IQR: 30.0-262.5). Robotic procedures included: pelvic tumor debulking 12 (75%), omentectomy 8 (50%), peritonectomy 6 (38%), large bowel resection 6 (37%), retroperitoneal mass resection 4 (25%), and hepatectomy 3 (19%). Median length of stay was 3.5 ds (IQR: 1.8-5.3) for the whole cohort and only 2 ds (IQR: 1.0-5.5) for patients who did not undergo hyperthermic intraperitoneal chemotherapy. Feasibility rate was 87.5%, whereas conversion, 30-d complication, and 30-d mortality rates were 12.5%, 18.8%, and 0%, respectively. CONCLUSIONS:Our experience with R-CRS demonstrates feasibility of the approach with a potential for benefit in short-term outcomes in a carefully selected cohort of patients when performed at a high-volume robotic surgery center.

Low-grade serous ovarian carcinoma (LGSOC) is a rare, treatment-resistant subtype of ovarian cancer characterized by peritoneal spread. Pressurized Intraperitoneal Aerosol Chemotherapy (PIPAC) delivers chemotherapy directly into the abdomen during serial laparoscopic surgeries, enabling repeated sampling of tumors for longitudinal analysis. Using single-nuclei RNA sequencing on 15 tumor samples across PIPAC cycles in two patients (a responder and a non-responder), we tracked molecular and cellular changes over time. Non-responder tumors showed upregulation of proliferation pathways (E2F, MYC, G2/M), KRAS signaling, epithelial-mesenchymal transition, and unfolded protein response, correlating with resistance. Responder tumors exhibited downregulation of proliferation and stress pathways but activated alternative survival mechanisms (PI3K, Wnt/β-catenin, Notch). Archetype analysis revealed dynamic shifts in metabolic and immune-related subpopulations in the responder tumors, while immunoprofiling showed greater immunosuppression in non-responder tumors. Despite the small cohort, these exploratory observations highlight tumor adaptation and underscore the need for multi-targeted therapies addressing proliferation, stress, survival, and immune evasion.

INTRODUCTION:The locoregional treatment of high grade serous ovarian cancer (HGSOC) comprises of cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC). Recent evidence form randomized trials, has led to controversy related to the use of HIPEC in addition to interval CRS (iCRS) and the role of secondary CRS (sCRS) in patients with the first platinum-sensitive recurrence from high-grade serous ovarian cancer (HGSOC). This multi-society consensus, coordinated by the Peritoneal Surface Oncology Group International (PSOGI) with inputs from ISSPP, SSO, ESSO, and IGCS, evaluated the role of these interventions using the GRADE ADOLOPMENT methodology. PATIENTS AND METHODS:An international expert panel reviewed evidence for the use of HIPEC in addition to iCRS in stage 3 high grade serous ovarian cancer (HGSOC) and the role of sCRS for patients with platinum-sensitive recurrent HGSOC. A systematic review assessed randomized controlled trials (RCTs) for recurrence-free survival (RFS), overall survival (OS), safety, and quality of life (QoL). Recommendations were formulated using the GRADE Evidence-to-Decision framework. RESULTS:HIPEC in addition to iCRS was strongly recommended based on the results of the OVHIPEC-1 trial, which showed significant benefit in RFS (3.5 months) and OS (12 months) without increasing the grade 3-4 morbidity. For the first platinum-sensitive recurrence, a conditional recommendation was made either for sCRS with systemic therapy or systemic therapy alone, reflecting variability in trial outcomes due to heterogeneity in the patient population in the trials and lack of surgical standardization. CONCLUSION:This consensus highlights the benefits of HIPEC in addition of iCRS and key factors that limit its wide-spread use. It underlines the need for individualized decision-making while selecting patients for sCRS. Future research integrating advanced systemic therapies is essential to refine these recommendations and provide equitable access to these complex locoregional treatments.

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Pterostilbene (3,5-dimethoxy-40-hydroxystilbene) is a potent oral antioxidant with a promising role in anti-cancer treatment. In endometrial cancer (EC), in vitro studies demonstrated a synergistic antiproliferative effect of pterostilbene (PT) with megestrol acetate (MA), a common treatment for EC. This is a randomized phase II clinical trial (NCT03671811) of PT+MA vs. MA for three weeks prior to scheduled hysterectomy. The primary objective is to determine the antiproliferative effect of PT+MA vs. MA using Ki-67 index. The secondary objectives are toxicity, histological response, transcriptional changes, and lipid metabolism. A total of 44 patients were enrolled between January 2019 and November 2022 with 23 randomized to Arm 1 (PT+MA) and 21 to Arm 2 (MA). Toxicities included one G3 thromboembolic event (PT+MA) and one G3 hypertension event (MA). Histological responses were high in both arms (>90%). There was no difference in Ki-67 changes, although, when restricted to endometroid subtype, the relative decrease in Ki67 was 33.8% in PT+MA vs. 20.1% in MA alone (p = 0.14). Whole transcriptomic gene profiling of samples before and after PT+MA exposure demonstrated the activation of interferon alpha response pathway and suppression of mTORC1 signaling, hypoxia, oxidative phosphorylation, and IL2-STAT5 signaling. Lipid metabolism analyses did not reveal any significant changes between arms. PT is well-tolerated in the preoperative treatment of EC and demonstrated in vivo anti-cancer effects on the transcriptomic level.

5569 Background: Hyperthermic intraperitoneal chemotherapy (HIPEC) is associated with improved overall survival in Stage III epithelial ovarian cancer (EOC) patients. We set out to evaluate the gene signatures associated with HIPEC response in EOC patients. Methods: Ninety-one EOC patients who underwent HIPEC with pre-operative tumor samples at City of Hope (51) and CHU Lyon (40) were identified between 2014 and 2022. RNA isolation was performed from formalin-fixed paraffin-embedded samples, followed by Whole-transcriptome library construction. Following exclusion of non-high grade serous (HGS) samples, and quality control steps, twenty-four samples were excluded. Progression-free survival (PFS) was used to define HIPEC response. Cut-off PFS values were used to distinguish good vs poor responders in primary EOC patients (18 months, based on KGOG, CARCINO-HIPEC trials), and recurrent EOC patients (12 months, based on MSK, CHIPOR HIPEC trials). Differential Gene Expression Analysis comparing good and poor HIPEC responders identified significantly changed genes. Pathway analysis was conducted using gene set enrichment analysis (GSEA) against Hallmark. Results: A total of sixty HGS tumor samples with available survival data were analyzed. 63.3% were primary EOC, 36.7% recurrent EOC. Germline BRCA mutations affected 21.7% of patients. With a median follow up of 31.9 months, median PFS was 29.3 (95%CI: 15.3, 63.5) months in primary EOC patients and 26.0 (95%CI: 14.7, 37.1) months in recurrent patients. Median OS was not reached in either group. 60.0% had a recurrence. Thirty-eight patients were identified as good responders, with a median PFS of 37.1 mos. (95%CI: 26.4, NR); 18 patients were identified as poor responders, with median PFS of 11.4 months (95%CI: 7.5, 14.2). Differential gene expression analysis between good and poor responders revealed 29 significantly upregulated 35 downregulated genes in HIPEC responders. Top upregulated genes in HIPEC responders include MAPK signaling pathway genes (RIB2, ETV5, CAPN8, IGFR1), in addition to CCND1 and CEACAM1. In HIPEC responders, the top-ranking gene sets in the transcriptional signature included Notch, KRAS, and Wnt/beta-catenin signaling pathways. In poor HIPEC responders, the DNA damage repair associated pathways E2F targets and G2M checkpoint, were activated. Similar transcriptomic pathway signatures were observed in Non-recurrent versus Recurrent HIPEC patients: Non-recurrent tumors were enriched with Notch signaling, while Recurrent tumors were enriched with E2F target and G2M checkpoint pathways. Conclusions: Good HIPEC response is characterized by transcriptional signatures consistent with Type I EOC characteristics of PI3K/RAS/Notch signaling. Recurrence after HIPEC in HGS ovarian cancer is higher in patients with E2F/G2M transcriptional signatures.

IntroductionLow grade serous ovarian carcinoma (LGSOC) is a rare subtype of ovarian cancer (OC) that is challenging to treat due to its relative chemoresistance. Given that LGSOC patients often recur in the peritoneal cavity, novel intraperitoneal (IP) chemotherapy should be explored. Pressurized intraperitoneal aerosolized chemotherapy (PIPAC) is a method that has demonstrated peritoneal disease control in cancers with peritoneal metastases.MethodsNCT04329494 is a US multicenter phase 1 trial evaluating the safety of PIPAC in recurrent ovarian, uterine, and GI cancers with peritoneal metastases. This analysis describes the outcomes of a sub-cohort of four LGSOC patients treated with IP cisplatin 10.5 mg/m2, doxorubicin 2.1 mg/m2 PIPAC q4-6 weeks. Primary endpoints included dose-limiting toxicities (DLT) and incidence of adverse events (AE). Secondary endpoints were progression free survival (PFS) and treatment response based on radiographic, intraoperative, and pathological findings.ResultsFour patients with LGSOC were enrolled of which three were heavily pretreated. Median prior lines of therapy was 5 (range 2-10). Three patients had extraperitoneal metastases, and two patients had baseline partial small bowel obstructive (SBO) symptoms. Median age of patients was 58 (38-68). PIPAC completion rate (≥2 PIPACs) was 75%. No DLTs or Clavien-Dindo surgical complications occurred. No G4/G5 AEs were observed, and one G3 abdominal pain was reported. One patient had a partial response after 3 cycles of PIPAC and completed an additional 3 cycles with compassionate use amendment. Two patients came off study after 2 cycles due to extraperitoneal progressive disease. One patient came off study after 1 cycle due to toxicity. Median decrease in peritoneal carcinomatosis index between cycles 1 and 2 was 5.0%. Ascites decreased in 2 out of 3 patients who had ≥2 PIPACs. Median PFS was 4.3 months (1.7-21.6), median overall survival was 11.6 months (5.4-30.1), and objective response rate was 25%.ConclusionPIPAC with cisplatin/doxorubicin is well tolerated in LGSOC patients without baseline SBO symptoms. IP response was seen in 2 out of 3 patients that completed ≥2 PIPAC cycles. Further study of PIPAC for patients with recurrent disease limited to the IP cavity and with no partial SBO symptoms should be considered.

Cytoreductive surgery (CRS) with or without hyperthermic intraperitoneal chemotherapy has become standard for resectable peritoneal surface malignancies. CRS aims to achieve complete resection of macroscopic disease through peritonectomy procedures and visceral resections. The pelvis is very frequently involved in peritoneal malignancies, making surgical techniques that ensure complete tumor removal an essential part of CRS. This is best achieved through an en bloc pelvic peritonectomy, which frequently includes a hysterectomy and bilateral oophorectomy in women. We created a video to review technical steps and exposure tips to achieve a complete cytoreduction of the pelvis in female patients with en bloc resection of the entire pelvic peritoneum, including the cul-de-sac, the uterus, and the adnexa, with (‘classic pelvic peritonectomy’) or without (‘visceral-sparing pelvic peritonectomy’) rectosigmoid resection. The creation of a protective ileostomy in classic pelvic peritonectomy is routine in many centers, while other centers advocate only selective and sparing use of ileostomy. In our center, protective ileostomy is used selectively and is therefore not included in the video. In the first part of the video, we review the rationale, indications, and steps, while in the second part, we show a practical demonstration of both a classic and a visceral-sparing pelvic peritonectomy in female patients. Complete pelvic peritonectomy can be achieved both with or without en bloc resection of the rectosigmoid colon. This technique is an essential part of CRS, and mastery of the technique can help the likelihood of achieving complete tumor removal in advanced or complex involvement of the pelvis.

Objective. Platinum-resistant epithelial ovarian cancer (EOC), recurrent endometrial cancer (EC), and triple negative breast cancer (TNBC) are difficult to treat after failing standard therapies. This phase I study evaluated mirvetuximab soravtansine (MIRV) and gemcitabine in patients with recurrent FR alpha-positive EOC, EC, or TNBC to determine the maximum tolerated dose (MTD)/recommended phase 2 dose (RP2D) (primary endpoint). Methods. FR alpha-positive patients with platinum-resistant EOC, EC, or TNBC with <= 4 prior chemotherapy regimens (2 for EC) were enrolled. FR alpha expression requirement varied among eligible tumors and changed during the study. Results. Twenty patients were enrolled; 17 were evaluable for DLT. Half the patients received >= 3 prior chemotherapy lines. Most EOC and EC patients (78%) were medium (50-74%) or high(75-100%) FR alpha expressors. TNBC patients were low (25-49%) FR alpha expressors. The MTD/RP2D was MIRV 6 mg/kg AIBW D1 and gemcitabine 800 mg/m2 IV, D1 and D8, every 21 days (Dose Level [DL] 3), where 5/7 patients demonstrated a partial response (PR) as their best response, including 2 confirmed ovarian responses whose time-to-progression and duration of response were 7.9/5.4 and 8.0/5.7 months respectively. Most common treatment-related adverse events at MTD were anemia and neutropenia (3/7 each, 43%), diarrhea, hypophosphatemia, thrombocytopenia, and leukopenia (2/7 each, 29%). DLTs were thrombocytopenia (DL1), oral mucositis (DL4) and diarrhea (DL4). Nine of 20 patients (45%; 95% CI: 21.1-68.9%) achieved PR as their best response, with 3/20 patients or 15% (95%CI, 0-32.1%) confirmed PR. Conclusion. MIRV and gemcitabine demonstrate promising activity in platinum resistant EOC at RP2D, but frequent hematologic toxicities.

Pressurized intraperitoneal aerosolized chemotherapy (PIPAC) is a novel, minimally invasive, safe, and repeatable method to treat carcinomatosis. Evidence regarding the clinical benefit (quality of life and survival) of PIPAC compared with that of conventional standard therapy (ST) is lacking. This is the secondary analysis of the phase 1 US-PIPAC trial for refractory colorectal and appendiceal carcinomatosis. A PIPAC cohort was compared with a retrospective cohort of consecutive patients receiving ST. The primary outcome was number of good days (number of days alive and out of the hospital). The secondary outcomes were overall survival (OS), progression-free survival (PFS), health-related quality of life (HRQoL), and objective functional recovery (daily step count). The study included 32 patients (PIPAC, 12; ST, 20) with similar baseline characteristics. Compared with the ST cohort, the PIPAC cohort had lower median inpatient hospital stays (> 24 h) within 6 months (0 vs 1; p = 0.015) and 1 year (1 vs 2; p = 0.052) and higher median good days at 6 months (181 vs 131 days; p = 0.042) and 1 year (323 vs 131 days; p = 0.032). There was no worsening of HRQoL after repeated PIPACs. Step counts diminished immediately after PIPAC but returned to baseline within 2–4 weeks. Kaplan–Meier analysis demonstrated a favorable association between receipt of PIPAC and OS (median, 11.3 vs 5.1 months; p = 0.036). Compared with ST, PIPAC was associated with higher number of good days, reduced hospitalization burden, and longer OS without a negative impact on HRQoL with repeated PIPACs. These findings are foundational for evaluation of PIPAC in a randomized clinical trial.

e17601 Background: The oral antioxidant pterostilbene (PT) (3,5-dimethoxy-40-hydroxystilbene) has demonstrated synergistic antiproliferative effect with megestrol acetate (MA) in endometrial cancer (EC). We conducted a preoperative (window of opportunity) study enrolling endometrial cancer patients scheduled for hysterectomy, who were randomized to preoperative PT+MA vs MA alone. Methods: This prospective, randomized phase II clinical trial (NCT03671811) enrolled patients who were surgical candidates for hysterectomy. Patients were randomized 1:1 to each arm and were treated for 3 weeks with either PT+MA (arm 1) or MA alone (arm 2). Exploratory objectives included histologic response by GOG 211 criteria, and transcriptional changes using whole transcriptome analysis. For the RNA-seq analysis, differential expression analysis used the “limma” R limma package. The differentially expressed genes were selected based on the cutoff values of p-value <= 0.05 and fold change >= 1.5. The gene set enrichment analysis was performed using GSEA software v. 4.3.2 to identify the affected Hallmark and KEGG pathways, using the pre-ranked gene list ranked by the -log10(p-value) with a sign determined by the fold change direction. Results: This prospective, randomized phase II clinical trial (NCT03671811) enrolled patients who were surgical candidates for hysterectomy. Patients were randomized 1:1 to each arm and were treated for 3 weeks with either PT+MA (arm 1) or MA alone (arm 2). Exploratory objectives included histologic response by GOG 211 criteria, and transcriptional changes using whole transcriptome analysis. For the RNA-seq analysis, differential expression analysis used the “limma” R limma package. The differentially expressed genes were selected based on the cutoff values of p-value <= 0.05 and fold change >= 1.5. The gene set enrichment analysis was performed using GSEA software v. 4.3.2 to identify the affected Hallmark and KEGG pathways, using the pre-ranked gene list ranked by the -log10(p-value) with a sign determined by the fold change direction. Conclusions: In endometrial cancer, the oral antioxidant Pterostilbene increases innate immune system pathway expression, while reducing mTOR pathway expression, potentially serving as a useful adjunct to progestin hormonal therapy in EC. Clinical trial information: NCT03671811 .

e17577 Background: Cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy improves survival in ovarian cancer patients. Currently, no biomarkers exist to select for patients who best benefit from HIPEC. We compared the slicing landscape of ovarian cancer tumors of good and poor HIPEC responders in a Phase I clinical trial, to identify potential predictive biomarkers. Methods: A total of 35 ovarian cancer patients enrolled in a Phase I HIPEC trial (NCT01970722), in which nine patients had paired pre-and post treatment tissue samples collected. Pre-HIPEC tumor samples had RNA isolated, and whole-transcriptome library construction performed. FASTQ files from tumor samples were aligned to GRCH38 and ran through SplAdder (PMID:26873928) to identify alternative splicing events. Outlier splice events were ranked by mean log-likelihood score and converted to amino acid sequences using Bisbee (PMID:34031440). The top 15 outlier events were run through NetMHCpan (PMID:32406916) and DeepHLApan (PMID:31736974) to predict putative neoantigens. Results: Among nine HIPEC-treated ovarian cancer patients with available RNAseq data, five were considered good responders (≥12months PFS), and four as poor responders (<12 months PFS). Alternative splicing analysis identified 519splice events as outliers between good and poor responders, with 250reported to be novel. Of the 250 novel splicing events, we identified a novel protein coding 3’ end splice event in CPNE1 which was alternatively spliced in at a Percent-Spliced-In (PSI) of 99% in three out four poor responders. The same splice event was alternatively spliced at a PSI of 30.3% in four out of five good responders. CPNE1 plays a role in calcium mediated intracellular processes, and is involved in the TNF-alpha receptor signaling pathway, thus playing an important role in cell proliferation, differentiation, apoptosis, and modulation of immune responses and induction of inflammation. The encoded novel peptide from the CPNE1 splice event produced six predicted strong binding sites based on a binding score>0.80 and an immunogenic score>0.80. Conclusions: CPNE1 was identified as a differentially spliced event in poor HIPEC responders with ovarian cancer. Poor HIPEC responders had higher immunogenic score. Alternative splicing analysis may be a promising method to determine potential biomarkers for HIPEC treatment in ovarian cancer patients. Clinical trial information: NCT01970722 .

Tumor heterogeneity is a significant factor influencing cancer treatment effectiveness and can arise from genetic, epigenetic, and phenotypic variations among cancer cells. Understanding how tumor heterogeneity impacts tumor evolution and therapy response can lead to more effective treatments and improved patient outcomes. Traditional bulk genomic approaches fail to provide insights into cellular-level events, whereas single-cell RNA sequencing (scRNA-seq) offers transcriptomic analysis at the individual cell level, advancing our understanding of tumor growth, progression, and drug response. However, implementing single-cell approaches in clinical trials involves challenges, such as obtaining high-quality cells, technical variability, and the need for complex computational analysis. Effective implementation of single-cell genomics in clinical trials requires a collaborative “Team Medicine” approach, leveraging shared resources, expertise, and workflows. Here, we describe key technical considerations in implementing the collection of research biopsies and lessons learned from integrating scRNA-seq into City of Hope’s clinical trial design, highlighting collaborative efforts between computational and clinical teams across breast, brain, and ovarian cancer studies to understand the composition, phenotypic state, and underlying resistance mechanisms within the tumor microenvironment.