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Review
. 2017 Nov 21;117(11):1583-1591.
doi: 10.1038/bjc.2017.356. Epub 2017 Oct 24.

TAMeless traitors: macrophages in cancer progression and metastasis

Shweta Aras  1 , M Raza Zaidi  1
Affiliations
Review

TAMeless traitors: macrophages in cancer progression and metastasis

Shweta Aras et al. Br J Cancer. .

Abstract

Macrophages are conventionally classified into M1 and M2 subtypes according to their differentiation status and functional role in the immune system. However, accumulating evidence suggests that this binary classification system is insufficient to account for the remarkable plasticity of macrophages that gives rise to an immense diversity of subtypes. This diverse spectrum of macrophage subtypes play critical roles in various homeostatic and immune functions, but remain far from being fully characterised. In addition to their roles in normal physiological conditions, macrophages also play crucial roles in disease conditions such as cancer. In this review, we discuss the roles tumour-associated macrophages (TAMs) play in regulating different steps of tumour progression and metastasis, and the opportunities to target them in the quest for cancer prevention and treatment.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Macrophage differentiation and their role in tumourigenesis. Classically activated (M1) macrophages are activated by IFN-γ, LPS or TLR ligands, secrete pro-inflammatory cytokines and play tumouricidal roles. Alternatively activated (M2) macrophages are activated by IL-4 and IL-13, secrete anti-inflammatory cytokines IL-10 and TGF-β and play tumourigenic roles. Tumour-associated macrophages (TAMs) display M2-like phenotype and exhibit pro-tumourigenic features.
Figure 2
Figure 2
The ‘binary’ vs ‘spectrum’ model of macrophage polarisation. Recent evidence strongly suggests that the conventional model of binary polarisation of macrophages into M1 and M2 subtypes is oversimplified and the molecular profile of several newly discovered subtypes of macrophages do not fit either phenotype. The spectrum model of macrophage polarisation suggests that there exist various subtypes of differentiated macrophages by virtue of an intricate network of transcriptional regulators, which participate in many homeostatic as well as pathological functions.
Figure 3
Figure 3
Role of TAMs in tumourigenesis. Different roles of TAMs in promoting tumour invasion and metastasis, along with the specific markers, are depicted. Tumour microenvironmental cues educate the macrophages to adopt a specific phenotype and perform distinct roles contributing towards tumourigenesis.
See this image and copyright information in PMC

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