Phase II single-arm, single-center clinical trial of all-trans-retinoic acid, bevacizumab, and atezolizumab in refractory microsatellite stable colorectal cancer.

Myeloid derived suppressor cells (MDSCs) are a heterogenous population of myeloid progenitor cells that suppress T cells and other potentially anti-cancer immune cells. MDSC presence in cancer patients can diminish immunotherapy response and worsen treatment outcomes. Here we examine a low-risk, low-cost approach to MDSC modulation by examining the impact of voluntary wheel-running exercise on MDSC populations in a Fisher-344 rat, MATBIII mammary adenocarcinoma model. Rat MDSCs in blood, spleen, bone marrow, and tumor tissue were identified by dual expression of surface markers His48 and CD11b and confirmed to be immunosuppressive upon sorting and interrogation in an in-vitro T cell suppression assay. We find that the percentage of MDSCs (as a proportion of total cells) is reduced in whole spleen isolates (2.55% vs. 19.68%, P≤0.005) and in the circulating white blood cell fraction (1.33% vs. 23.21%, P≤0.05) of exercised versus sedentary animals. In contrast, we find no difference between the proportion of MDSCs as a population of total cells in bone marrow (23.57% vs. 25.52%, P≥0.05) or tumor tissue (11.68% vs. 7.10%, P≥0.05). We conclude that exercise decreases splenic and circulating MDSC populations in tumor bearing animals. Further studies are necessary to establish the molecular mechanisms of this suppression to leverage potential interactions between exercise and MDSC-directed immune therapies.

Introduction: Myeloid-derived suppressor cells (MDSCs) constitute a heterogeneous population that plays a key role in tumor-related immune suppression. MDSCs are immature cells that express the myeloid markers CD11b and Gr1 in mice and accumulate in tumor-bearing mice, including those with HER2/neu+ breast cancer. We previously reported that tumor regression by anti-neu antibodies requires both innate and adaptive immunity. MDSCs inhibit both types of immunity and are immunosuppressive, particularly for T cells. However, the effect of anti-neu antibodies on MDSCs remains unclear. Methods: HER2+ TUBO tumor-bearing mice were treated with an anti-neu antibody or a control. MDSC populations were analyzed via flow cytometry, and immunosuppressive function was analyzed by a suppression assay. Tumors were analyzed using an RT2-PCR array and RT-PCR for gene expression related to MDSC activation, migration, and function. Additional mice received combination therapy with 5-FU or zoledronic acid to assess enhanced MDSC inhibition and changes in MDSC and tumor-associated macrophage (TAM) populations. Results: The number of MDSCs decreased within 3 days after anti-neu antibody treatment in the tumor and spleen, with the number of tumor MDSCs declining 1 day earlier. The number of monocytic MDSCs was significantly reduced in both tissues (p > 0.05). Anti-neu antibodies also reduced MDSC immunosuppressive activity. Gene expression analysis revealed decreased levels of IL-1β, VEGF, and CX3CL1, which are linked to MDSC activation and migration. The level of the immunosuppressive factor indoleamine 2,3-dioxygenase was also reduced. Compared with treatment with the antibody alone, combination therapy with 5-FU further suppressed the number of MDSCs and TAMs, resulting in better tumor suppression. Conclusions: Tumor suppression by anti-neu antibodies is associated with a reduction in MDSCs via the inhibition of key MDSC-related factors. MDSCs may be therapeutic targets for increasing Herceptin efficacy in patients with breast cancer.

Treatment with Acalibrutinib, Ibrutinib and CD19 CAR T Cells Restore the Number of Granulocytic Myeloid Derived Supressor Cells in CLL-Bearing Mice

The role of MDSCs in hepatocellular carcinoma – in vivo veritas?

A New Population of Myeloid-Derived Suppressor Cells in Hepatocellular Carcinoma Patients Induces CD4+CD25+Foxp3+ T Cells

Mass Cytometry Identifies a Novel Signature for Myeloid-Derived Suppressor-Cells in Waldenstrom's Macroglobulinemia

436 Background: MDSC have been linked to the chronic inflammatory microenvironment of tumor cells and pathologic outcomes in UC patients (pts) undergoing cystectomy. NLR is an established inflammatory biomarker with prognostic properties in mUC. We hypothesized that MDSCs correlate with NLR and OS in mUC. Methods: MDSCs were measured in blood samples from mUC patients by fresh unfractionated whole blood (WB) and peripheral blood mononuclear cells (PBMC). MDSCs were identified by flow cytometry in WB and defined as LinloCD33+/HLADR- (Total MDSC). MDSC subsets were defined as polymorphonuclear (PMN-MDSC: CD15+/CD14-), monocytic (M-MDSC: CD15-/CD14+), and uncommitted (UC-MDSC: CD15-/CD14-). MDSC populations were presented as % of live nucleated blood cells from PB and absolute numbers from WB. Spearman’s correlation assessed correlations between MDSC & NLR. Kaplan Meier curves and log rank test estimated OS from the time of MDSC collection to last follow up or date of death. Results: Of 79 pts, 77% were men and 42% were never smokers with a median age of 69 (31-83). Overall, 71% had pure UC and 81% had lower tract UC. Prior therapies include intravesical therapy (22%), neoadjuvant chemotherapy (31%), and cystectomy/nephroureterectomy (61%). Median follow up was 12 months (range: 0.6-36.5). PMN-MDSC was the predominant subset in WB and PBMC. There was significant correlation between individual MDSC subsets in WB and PBMC (p≤0.001). Negative correlation was noted between NLR and WB UC-MDSC:PMN-MDSC ratios (rho = -0.27, p = 0.03), as well as NLR and PB UC-MDSC:PMN-MDSC (rho = -0.28, p = 0.02). Median survival was 17.7 months (95% CI: 11.0-NA months). Overall 1-yr and 3-yr survival were 0.60 (95% CI: 0.49-0.73) and 0.15 (95% CI: 0.03-0.67), respectively. Higher WB UC-MDSC levels were associated with shorter OS (HR 2.85, 95% CI: 1.43-5.65, p = 0.003). Conclusions: Specific MDSC subsets correlate with NLR. Higher WB UC-MDSC levels have negative prognostic roles for OS. Given the feasibility of serial blood draws, dynamic assessment of MDSC over time and further validation with longer follow up are needed.

434 Background: MDSC are a heterogeneous population of potent immunosuppressive cells with potential predictive/prognostic significance in solid tumors. The association between MDSC and clinicopathologic features in patients (pts) with UC was investigated. Methods: Peripheral blood from 26 non-metastatic UC pts scheduled to undergo cystectomy or nephroureterectomy at Cleveland Clinic was collected. MDSC were enumerated in fresh unfractionated blood (WB) and in peripheral blood mononuclear cells (PBMC). (T)otal MDSC were defined as CD33+/HLADR-; out of T-MDSC, (G)ranulocytic (CD15+CD14-), (M)onocytic (CD15-CD14+) and (I)mmature (CD15-CD14-) MDSC were identified. CD11b MDSC (Linlo/HLADR-/CD33+/CD11b+) were identified in WB. MDSC populations were presented as % of live nucleated blood cells and as absolute numbers from WB. Wilcoxon rank sum test was used to assess associations between MDSC populations and clinicopathologic features. Due to the exploratory nature of the study, p < .10 was considered significant. Results: Of 26 pts, 25 had surgery and 1 is under surveillance. 24 had both WB and PBMC data. 23/26 were men; median age 67. Of 26 pts, all had primarily UC histology; 7 had mixed UC histology, 11 had prior intravesical BCG, 12 neoadjuvant therapy (10 Gem/Cis, 1 Gem/Carbo, 1 unknown). Of 25 pts who had surgery, 5 had pT3/4 stage; 5 had LVI; 9 had CIS. All but 1 had negative LN. Higher levels of specific WB MDSC populations were associated with mixed histology (including squamous), CIS, and higher pT-stage (Table). When compared to a separate cohort of 11 pts with metastatic UC, the % G-MDSC in PBMC was lower in non-metastatic pts (median 0.3 vs. 1.47; p = .05). Conclusions: Although no single MDSC population correlated with all the evaluated clinicopathologic features, higher levels of certain MDSC populations appear to correlate with histology and pT stage. Further validation of blood and tissue is ongoing in a larger cohort. [Table: see text]

4548 Background: MDSC are potent immunosuppressive cells with prognostic implications in many solid tumors. We previously reported significant correlations between MDSC and clinicopathologic features in localized UC. We hypothesized that different MDSC populations may correlate with inflammatory biomarkers and clinicopathologic features in mUC. Methods: Peripheral blood samples were collected from 46 mUC pts. MDSCs were measured in fresh unfractionated whole blood (WB) and in peripheral blood mononuclear cells (PBMC). MDSCs were identified by flow cytometry in WB and defined as LinloCD33+/HLADR- [(T)otal MDSC]. MDSC subsets were defined as (G)ranulocytic (CD15+CD14-), (M)onocytic (CD15-CD14+), (I)mmature (CD15-CD14-), or CD11b+. MDSC populations were presented as % of live nucleated blood cells and as absolute numbers from WB. Spearman correlations (r) and Wilcoxon rank sum test were used to assess correlations between MDSC populations & clinicopathologic factors. Results: Of 46 pts:78% men, median age at diagnosis 69 (31-83), 33% never smokers, 76% pure UC, 76% bladder primary, 28% prior intravesical therapy, 35% prior neoadjuvant chemotherapy, 56% prior cystectomy, 83% overweight/obese. G-MDSC was the predominant subset in WB (43%) and PBMC (39%), although M-MDSC were almost equally predominant in PBMC (35%). There was a correlation between the WB and PBMC values of T-, I-, and M- MDSC (p≤0.05). Higher % WB I-MDSC correlated with lower blood neutrophil/lymphocyte ratio (NLR) (p = 0.009), while higher WB G-MDSC and %PBMC G-MDSC were associated with higher NLR (p = 0.03 and p = 0.02, respectively). Higher I-MDSC / G-MDSC ratio was associated with lower NLR (r = -0.35, p = .02) and with various clinicopathologic parameters. Conclusions: HigherI-MDSC / G-MDSC ratio correlates inversely with NLR, which is considered an inflammatory biomarker and had prognostic value in other studies. The mechanism of MDSC interaction with inflammatory response in mUC pts merits evaluation and is being investigated in a larger cohort of UC pts on chemotherapy or immunotherapy (with longer follow up).

BackgroundPancreatic Ductal Adenocarcinoma (PDAC) has very poor 5-year overall survival rate. Despite the encouraging effect of immunotherapy in other cancer types, clinical benefit in PDAC patients remains limited. One of the reasons for the lack of success is the immunosuppressive tumor microenvironment (TME), which is maintained by myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages. High MDSC infiltration is associated with a poor survival in PDAC patients. Our project aims at identifying tumor-driven chemokines that influence recruitment of MDSC and establishment of the immunosuppressive tumor microenvironment.Materials and Methods45 PDAC cell lines generated from spontaneous tumors of genetically-modified mice harboring the characteristic driver mutations KrasG12D or PIK3CAH1047R were analyzed for their expression levels of CXCL1, CCL2, G-CSF and GM-CSF by qRT-PCR. In order to study the relationship between the chemokine/cytokine profile and the immune cell infiltration, selected tumor cell lines were implanted orthotopically in C57BL6 mice. Three weeks after inoculation blood, spleen and tumor were isolated and organ specific immune cell infiltration was analyzed by flow cytometry. To further characterize tumor-secreted factors tumor conditioned medium was generated and the concentration of 33 chemokines was analyzed in a multiplex assay. The chemokine levels were correlated with migratory capacity of splenic MDSC measured in an ex vivo chemotaxis assay.ResultsCXCL1 significantly enhanced migration of polymorphonuclear MDSC (PMN-MDSC) in vitro, while migration of monocytic MDSC (M-MDSC) was predominantly skewed towards CCL2. Three weeks after tumor inoculation, MDSC populations in blood and spleen were expanded. Most intriguingly, PDAC cell lines with high CXCL1 or CCL2 levels in vitro showed significantly enriched intratumoral accumulation of PMN-MDSC and M-MDSC, respectively, suggesting that tumor-intrinsic chemokine secretion and not factors from the tumor stroma determined MDSC infiltration. The ex vivo chemotaxis assays revealed additional factors that modulate migration of MDSC into the TME.ConclusionsThe in vitro gene expression levels of individual chemokines (CXCL1 and CCL2) determines the MDSC infiltration in vivo into the TME. Targeting the chemokine-receptor axis of MDSC subpopulations could be a promising approach in the treatment of pancreatic cancer.FundingThe project was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Projektnummer 329628492 - SFB 1321 and the Förderprogramm für Forschung und Lehre (FöFoLe) funded by the Ludwig-Maximilians-Universität München.Disclosure InformationC. Rambuscheck: None. P. Metzger: None. C. Hörth: None. R. Hennel: None. S. Bärthel: None. C. Falcomatà: None. K. Lauber: None. S. Endres: None. D. Saur: None. M. Schnurr: None. L.M. König: None.

Glioblastoma (GBM) development and therapeutic resistance has been accompanying with the tumor-associated macrophages (TAMs) in the tumor microenvironment (TME). TAMs are heterogeneous cell populations of immune regulatory myeloid-derived suppressor cells (MDSCs) and polarization of anti-tumor macrophages (M1) into pro-tumor macrophages (M2). We investigated the role of myeloid cell NF-κB signaling in orthotopic GBM model using immune deficient and immune competent hosts. Interestingly, conditional deletion of canonical NF-κB signaling (p65) with Lysm-Cre (p65 KO) in myeloid cells, significantly inhibited syngeneic GL261 tumor growth in immune-competent mice compared to control mice. We studied the TAMs recruitment to the tumor and their polarization under the influence of TME. P65 KO mice displayed decreasing trend of immune cell infiltration (CD45), which phenotyped as decreased F4/80+, CD68+, CD206+ (M2) and Gr1+CD11b+ (MDSCs) macrophages, compared to control mice. This was associated with the increased CD80+ (M1) macrophages, increasing trend of CD4+ and CD8+ cytotoxic T cells, and decreased CD44+ mesenchymal cancer stem cells (CSCs) populations in the TME. Cytokine array data indicated that loss of canonical NF-κB signaling within the TAMs was implicated in increased production of IFNγ, IGF1, MCP1, MIP1α, and TNFα cytokines. Co-culture of T cells with p65 KO or control MDSCs identified increased proliferation of T cells with p65 KO MDSCs compared to control MDSCs. Conversely, GBM patient-derived xenografts and U251 GBM cell line-derived tumors showed increasing trend of growth in immune-deficient mice, following the transplantation of p65 KO bone marrow (BM) compared to control BM. Pro-tumor macrophages and CSCs were increased and T cell populations were decreased in human tumors grown in immune deficient mice transplanted with p65 KO BM, compared with control BM. In addition, analysis of human data set revealed higher expression of p65 subunit of NF-κB complex in brain tumor stroma compared to the tumor cells. The study suggests that canonical NF-κB signaling in TAMs is required for the tumor-promoting macrophage polarization and GBM growth in immunocompetent host compared to immune deficient host. Therefore, targeting myeloid-specific NFκB signaling in GBM could inhibit the immune suppressive TAMs and improve the anti-tumor immunity. Citation Format: Bhagelu R. Achyut, Jennifer Bradford, Kartik Angara, Mohammad Rashid, Meenu Jain, Thaiz Borin, ASM Iskander, Roxan Ara, Ali Arbab. Canonical NFkB signaling in myeloid cells is required for the glioblastoma growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3968. doi:10.1158/1538-7445.AM2017-3968

Introduction: Ovarian cancer (OC) remains the deadliest gynecologic malignancy, with minimal improvement in the 5-year survival rate over the past three decades despite advancements in treatment. High-grade serous ovarian cancer (HGSOC) is characterized by aggressive progression, driven by elevated secretion of extracellular vesicles (EVs), tumor-associated macrophage (TAM) activation, and increased myeloid-derived suppressor cell (MDSC) populations. These factors contribute to immune suppression, metastasis, and poor patient outcomes. Here, we report on a novel small-molecule inhibitor, HO-4200, which modulates macrophage polarization and suppresses MDSCs within the ovarian tumor microenvironment. Methods: EV quantification and size characterization were performed using nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM). In vivo studies using immunocompetent mice evaluated HO-4200's anticancer efficacy. Macrophage polarization and MDSC populations were analyzed via flow cytometry. The effects of HO-4200 on ovarian cancer and primary ascites-derived cell lines were examined in vitro. Additionally, expression levels of EV secretion pathway proteins TMEM205 and Rab27a were measured by ELISA and RT-PCR. Results: HO-4200 demonstrated significant antiproliferative effects, reducing ovarian cancer cell viability by 60-75% at concentrations of 2-5 µM after 48 hours. HO-4200 also inhibited the expression of EV secretion pathway proteins TMEM205 and Rab27a in ovarian cancer cells. Mechanistic studies revealed that HO-4200 promoted M1 macrophage polarization and reduced MDSC populations in vitro and in vivo immunocompetent mouse models. These findings suggest that HO-4200 suppresses EV secretion, thereby enhancing antitumor immune responses and reducing tumor progression and metastasis in ovarian cancer. Conclusion: This study provides the first evidence that HO-4200 inhibits ovarian cancer cell proliferation, promotes M1 macrophage polarization, and reduces MDSC populations by targeting EV secretion pathway proteins. These results highlight the therapeutic potential of HO-4200 in modulating the immune microenvironment and combating ovarian cancer progression and metastasis. Citation Format: Ganesh Yadaigiri, Kalpana Deepa Priya Dorayappan, Lakshmi Narasimhan Chakrapani, Shyam Sundaram, Jessica Velasquez, Casey Cosgrove, David M. O’Malley, David E. Cohn, Selvendiran Karuppaiyah. A novel small molecule inhibitor, HO-4200, modulates macrophage polarization and suppresses MDSCs to enhance antitumor immune responses in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1772.

362 Background: MDSC are heterogeneous immunosuppressive cells with potential predictive/prognostic role in cancer. The association between MDSC, clinicopathologic factors and pathologic response in pts with UC merits evaluation. Methods: Peripheral blood and/or tissue was collected from 120 pts. MDSC were measured in fresh unfractionated whole blood (WB), in peripheral blood mononuclear cells (PBMC) and fresh tumor tissue. MDSCs were identified by flow cytometry in WB and defined as LinloCD33+/HLADR- ((T)otal MDSC). MDSC subsets were defined as LinloCD33+/HLADR- and (G)ranulocytic (CD15+CD14-), (M)onocytic (CD15-CD14+), (I)mmature (CD15-CD14-, CD11b+ ). MDSC populations were presented as % of live nucleated blood cells and as absolute numbers from WB. Spearman correlations (r) and Wilcoxon rank sum test were used to assess correlations between MDSC populations, clinicopathologic factors and pT0N0%. Results: Of 120 pts, 82 were non-metastatic: 58 had only blood, 23 had blood & tissue, 1 had only tissue available for analysis. Of these 82 non-metastatic pts, 70 were men, median age 68; 81 pts had primary UC histology, 1 small cell cancer, 24 had mixed UC histology; 24 had prior intravesical therapy, 34 had neoadjuvant therapy (79% cisplatin-based, 21% unknown), 4 pts had post-op recurrence. At cystectomy: 15/82 pT0, 22/82 pT3/4; 37/82 CIS; 8/78 pN+. Significant associations were seen between MDSC blood levels and mixed histology, CIS, pN+, and lower pT0N0% (Table). Tumor M-MDSCs were associated with pN+ (p=0.05). There was significant correlation between tumor and WB % M-MDSC (r=0.55, p=0.007), and tumor and WB % G-MDSC (r=0.46, p=0.03). Conclusions: Blood MDSC levels correlate with several clinicopathologic factors and may predict pathological complete response (pT0N0). Assessment of association between MDSC levels, outcome and immunotherapy response is ongoing including in metastatic pts. [Table: see text]

e16005 Background: MDSC are a heterogeneous population of immunosuppressive cells with potentially predictive implications in UC pts receiving CI. We hypothesized that MDSC populations may change after CI exposure. Methods: Serial peripheral blood samples were collected from mUC pts treated with CI. MDSC were measured in fresh unfractionated whole blood (WB) and in peripheral blood mononuclear cells (PBMC). MDSC were identified by flow cytometry in WB and defined as LinloCD33+/HLADR- [(T)otal MDSC]. MDSC subsets were defined as (G)ranulocytic (CD15+CD14-), (M)onocytic (CD15-CD14+), (I)mmature (CD15-CD14-), or CD11b+. MDSC populations were presented as % of live nucleated blood cells and as absolute numbers from WB. The Wilcoxon signed rank and rank sum tests were used to assess changes in MDSC populations while on CI. Results: 17 pts treated with CI (9 atezolizumab [A], 8 pembrolizumab [P]) had ≥ 2 MDSC samples for analysis. Median age at diagnosis was 71 (46-81), 12 men, 29% never smokers; 53% / 29% / 18% ECOG PS 0/1/2 and 59% visceral metastasis at the time of 1st sample collection. 10 pts received CI as 1st line therapy (Tx) in metastatic setting; 7 pts received chemotherapy as 1st-line Tx for mUC (6 platinum-based, 1 docetaxel) and CI as 2nd-line Tx. In 16 pts with samples before 1stdose, there was a relative decrease (median 36.3%, range -59.7 to +21.2) in PBMC % I-MDSCs between 1st and 2nd samples (p=0.06). Interestingly, PBMC %M-MDSC and %I-MDSC tended to increase compared to baseline in pts treated with P, while they tended to decrease in pts treated with A (Table). Conclusions: In this cohort of pts with mUC treated with CIs,MDSC changes differed based on CI (anti-PDL1 or anti-PD1). Further study in larger cohort with various prior Tx lines and longer follow up as well as correlations with Tx response, toxicity and outcomes are ongoing. [Table: see text]

e15573 Background: The most effective treatment of immune checkpoint inhibitors (ICIs) is restricted in microsatellite instability (MSI-H) subsets of advanced colorectal cancer, but MSI-H only accounts for 4-5% among them. Currently, Fruquintinib/ Regorafenib is the standard third-line treatment for metastatic colorectal cancer (mCRC) with microsatellite stable (MSS), which efficacy remains limited in pre-clinical trials. According to the published literature, ICIs has little efficacy in the treatment of refractory advanced mCRC patients with MSS. However, there may be a good synergistic mechanism in the combination of ICIs and anti-VEGFR drugs, which can improve the tumor microenvironment (TME). Our study aimed to evaluate the efficacy and safety of Fruquintinib plus Toripalimab as third-line treatment for refractory advanced mCRC. Methods: This was a single-arm, single-center, phase II clinical trial with 30 patients. Pts received toripalimab (240mg, i.v., Q3W), combined with Fruquintinib (5mg, p.o., 3 weeks on/ 1 week off) until the disease progresses/unacceptable toxicity or receiving the above two drugs as maintenance treatment. The primary endpoint was objective response rate (ORR); the secondary endpoints were disease control rate (DCR), 1-year progression-free survival (PFS) rate, overall survival (OS) and safety. Results: As of Feb 5, 2022, 24 mCRC pts (female: 29.2%, median age: 52.1 years) with ECOG PS ≤ 2 who failed to at least 2 previous lines of therapy containing fluoropyrimidine, oxaliplatin or irinotecan combined with Bevacizumab or Cetuximab were enrolled. The ORR was 16.7% (95% CI：59.7%-94.8%). The DCR was 54.1%, including 4 patients with PR and 9 patients with SD, respectively. 16 patients were alive and the study treatments for 6 patients were still ongoing. Median PFS was 6.0 months (95% CI：3.511-12.489), the 1-year PFS rate was 18%; median OS was 8.0 months (95% CI：1.452-10.548). Overall, 24 pts were enrolled for safety analysis, The most frequent treatment related adverse events were fatigue (50%), hepatocyte dysfunction (36.3%), hypertension (29.1%) and abdominal pain (27.0%). 6 patients (25%) experienced grade 3/4 TRAE (including hypertension, liver enzyme elevation, and immune-associated pneumonia). No treatment-related death was reported. TRAEs leading to either Fruquintinib or Toripalimab discontinuation occurred in 3 (12.5%) pts each. Conclusions: Fruquintinib plus Toripalimab showed certain efficacy and favorable safety profile in refractory advanced mCRC with MSS. It may provide a new choice for mCRC patients who are receiving third-line treatment. The results supported ongoing combined treatment in mCRC patients with MSS and more data will being updated subsequently. Clinical trial information: ChiCTR2000028965.