The mechanisms by which a primary tumor affects a selected distant organ before tumor cell arrival remain to be elucidated. This report shows that Gr-1+CD11b+ cells are significantly increased in lungs of mice bearing mammary adenocarcinomas before tumor cell arrival. In the premetastatic lungs, these immature myeloid cells significantly decrease IFN-γ production and increase proinflammatory cytokines. In addition, they produce large quantities of matrix metalloproteinase 9 (MMP9) and promote vascular remodeling. Deletion of MMP9 normalizes aberrant vasculature in the premetastatic lung and diminishes lung metastasis. The production and activity of MMP9 is selectively restricted to lungs and organs with a large number of Gr-1+CD11b+ cells. Our work reveals a novel protumor mechanism for Gr-1+CD11b+ cells that changes the premetastatic lung into an inflammatory and proliferative environment, diminishes immune protection, and promotes metastasis through aberrant vasculature formation. Thus, inhibition of Gr-1+CD11b+ cells could normalize the premetastatic lung environment, improve host immunosurveillance, and inhibit tumor metastasis. Cancer Res; 70(15); 6139–49. ©2010 AACR.

Triple-negative breast cancer (TNBC) is an aggressive subtype characterized by extensive intra-tumoral heterogeneity, and frequently develops resistance to therapies. Tumor heterogeneity and lack of biomarkers are thought to be some of the most difficult challenges driving therapeutic resistance and relapse. This review will summarize current therapy for TNBC, studies in treatment resistance and relapse, including data from recent single cell sequencing. We will discuss changes in both the transcriptome and epigenome of TNBC, and we will review mechanisms regulating the immune microenvironment. Lastly, we will provide new perspective in patient stratification, and treatment options targeting transcriptome dysregulation and the immune microenvironment of TNBC patients.

Transforming growth factor (TGF)-β is a multifunctional cytokine that has important roles in tumor formation, progression, and metastasis. TGF-β is overproduced, and its signaling is deregulated, in a variety of human tumors, including colorectal, gastric, pancreatic, and liver. Therapeutics are being developed to block TGF-β signaling. However, TGF-β also functions as a tumor suppressor in premalignant cells. It is not clear how its function changes from that of a tumor suppressor to a tumor promoter; improvements are needed in our understanding of TGF-β functions in tumor development before we can design inhibitors for use as anticancer therapies. TGF-β regulates not only different tumor-cell autonomous signaling pathways, but also interactions between tumor and host cells, through paracrine mechanisms. We review recent findings about how TGF-β is regulated and its roles in the tumor microenvironment and metastasis, with a focus on gastrointestinal cancers. Improved understanding of TGF-β regulation and how it mediates interaction between cancer epithelial cells, immune cells, and fibroblasts will provide important insights into tumor development and progression.

TGF-β is overexpressed in advanced human cancers. It correlates with metastasis and poor prognosis. However, TGF-β functions as both a tumor suppressor and a tumor promoter. Here, we report for the first time that genetic deletion of Tgfbr2 specifically in myeloid cells (Tgfbr2^MyeKO) significantly inhibited tumor metastasis. Reconstitution of tumor-bearing mice with Tgfbr2^MyeKO bone marrow recapitulated the inhibited metastasis phenotype. This effect is mediated through decreased production of type II cytokines, TGF-β1, arginase 1, and inducible nitric oxide synthase, which promoted IFN-γ production and improved systemic immunity. Depletion of CD8 T cells diminished the metastasis defect in the Tgfbr2^MyeKO mice. Consistent with animal studies, myeloid cells from patients with advanced-stage cancer showed increased TGF-β receptor II expression. Our studies show that myeloid-specific TGF-β signaling is an essential component of the metastasis-promoting puzzle of TGF-β. This is in contrast to the previously reported tumor-suppressing phenotypes in fibroblasts, epithelial cells, and T cells. Significance: Our study identifies myeloid-specific TGF-β signaling as a critical mediator in tumor metastasis, distinct from the tumor-suppressive effect of TGF-β signaling in epithelial cells, fibroblasts, and T cells. We further provide mechanistic insight into host antitumor immunity and suggest a cell type–specific cancer-targeting strategy. Cancer Discov; 3(8); 936–51. ©2013 AACR. See related commentary by Souza-Fonseca-Guimaraes and Smyth, p. 846 This article is highlighted in the In This Issue feature, p. 826