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Purpose: Determinants of treatment outcomes to chemotherapy-based regimens in metastatic pancreatic ductal adenocarcinoma (PDA) remain ill-defined. Our aim was to examine tissue-based correlates of treatment response and resistance using matched baseline and on-treatment biopsies collected from patients with PDA treated in the first-line metastatic setting., Experimental Design: Patients with treatment-naïve metastatic PDA were enrolled in a Phase II trial (NCT02077881) investigating gemcitabine plus nab-paclitaxel in combination with indoximod, an orally administered small-molecule inhibitor of the IDO pathway. Baseline and on-treatment biopsies (week 8) of metastatic lesions (88% liver) were collected from a cohort of responders (N = 8) and non-responders (N = 8) based on RECIST v1.1 and examined by multiplex IHC and mRNA sequencing., Results: Treatment altered the transcriptional profile of metastatic lesions with a decrease in tumor cell proliferation independent of treatment response. The antiproliferative response was seen in both basal and classical PDA subtypes. PDA subtype was not associated with survival outcomes; instead, genes involved in immune activation distinguished responders from non-responders. Tumor response was associated with an increase in CD3+ and CD8+ T-cell infiltrates into metastatic lesions. A composite of decreased tumor proliferation in response to treatment and increased CD8 T-cell infiltration in metastatic lesions identified responders and associated with a favorable survival outcome., Conclusions: Our findings suggest that inhibiting cancer cell proliferation alone in PDA is insufficient to produce tumor responses and support a role for tumor-extrinsic mechanisms, such as CD8+ T cells, which combine with the cancer cell proliferation index to define treatment outcomes., (©2023 American Association for Cancer Research.)

Pancreatic ductal adenocarcinoma (PDAC) shows remarkable propensity to metastasize. This predilection to escape from the primary tumor is driven by paracrine and autocrine mechanisms that guide cancer cells through a multi-step process concluding with colonization in distant tissues. Although cell-intrinsic features support the metastatic ability of cancer cells, permissive microenvironments within the primary organ and at sites of distant metastasis may be rate-limiting. Identification of cancer cell-extrinsic factors that regulate formation of these environments lend new therapeutic targets for intervening on the metastatic cascade. In addition, the bipolar, yet fundamental, role of the immune system in the metastatic process presents therapeutic opportunities. Herein, we review the current knowledge of the metastatic cascade in PDAC, and propose that genomically stable determinants of metastasis (e.g. the pro-metastatic niche and immune system) are actionable targets for preventing, containing, and treating metastasis in PDAC., Competing Interests: Declaration of Competing Interest G.L.B. is a consultant/advisory board member for Seattle Genetics, Aduro Biotech, AstraZeneca, Bristol-Myers Squibb, Incyte, Genmab, Takeda, Merck, and BiolineRx; reports receiving commercial research grants from Incyte, Bristol-Myers Squibb, Verastem, Halozyme, Biothera, Arcus, Newlink, Novartis, and Janssen; and is an inventor of intellectual property and recipient of royalties from Novartis and Advaxis, Inc. No potential conflicts of interest were disclosed by the other authors., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

The immune reaction to pancreatic ductal adenocarcinoma (PDAC) is a strong prognostic determinant of clinical outcomes and may be a promising therapeutic target. We use multiplex immunohistochemistry to illustrate distinct patterns of T-cell and myeloid cell infiltration seen in PDAC that have therapeutic implications and discuss the current state of immunotherapy in this disease. Based on collective findings from clinical and preclinical studies, two conceptual models have emerged for applying immunotherapy in PDAC that involve (1) restoring elements of T-cell immunosurveillance and (2) redirecting myeloid cells to condition tumors with increased sensitivity to cytotoxic therapies. Overall, the success of immunotherapy in PDAC will most likely rely on strategic combinations of therapies that are informed by well-designed correlative analyses that consider the spatial heterogeneity of immune responses detected in malignant tissues.

Cancer-associated inflammation is thought to be a barrier to immune surveillance, particularly in pancreatic ductal adenocarcinoma (PDA). Gr-1(+) CD11b(+) cells are a key feature of cancer inflammation in PDA, but remain poorly understood. Using a genetically engineered mouse model of PDA, we show that tumor-derived granulocyte-macrophage colony-stimulating factor (GM-CSF) is necessary and sufficient to drive the development of Gr-1(+) CD11b(+) cells that suppressed antigen-specific T cells. In vivo, abrogation of tumor-derived GM-CSF inhibited the recruitment of Gr-1(+) CD11b(+) cells to the tumor microenvironment and blocked tumor development-a finding that was dependent on CD8(+) T cells. In humans, PDA tumor cells prominently expressed GM-CSF in vivo. Thus, tumor-derived GM-CSF is an important regulator of inflammation and immune suppression within the tumor microenvironment., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The resurgent theory of cancer immunosurveillance holds that the immune system plays an important role in the suppression of tumors, particularly in the elimination of early neoplastic lesions. Tumors with reduced immunogenicity or those that have acquired mechanisms to suppress immune effector functions, however, can emerge from this selection pressure and grow progressively. This is an especially important issue in pancreatic cancer, which although inflammatory in vivo is nevertheless highly aggressive and nearly always lethal. Here, we review emerging data obtained from novel genetically defined mouse models of pancreatic adenocarcinoma that suggest that the immune system may be complicit in the inception and progression of pancreatic cancer. Host immune cells with suppressive properties infiltrate the pancreas early during tumorigenesis, even at the earliest stages of neoplasia, preceding and effectively undermining any lymphocytes with potential antitumor function. Thus, in pancreatic adenocarcinoma, the failure of immunosurveillance is likely an early event during tumorigenesis, a concept that carries important implications for the design of novel immunotherapeutics in this disease.