In March 2020, the European, American and Portuguese Associations for Cancer Research (EACR, AACR and ASPIC, respectively) held a basic and translational research conference on the tumour microenvironment (TME) that brought together more than 600 participants in Lisbon (Portugal). The inability of some speakers to travel owing to precautions relating to COVID-19 was not an obstacle: several excellent talks were delivered remotely.

Interrogating the analysis of the complex interactions between diverse cell types in the TME requires sensitive and reproducible methods, hence many talks focused on various modalities of single-cell analysis as well as multiplex and intravital imaging. The improved performance of these techniques over the past few years has not only enabled the separation of cell subpopulations on the basis of their molecular features, but also their dynamic monitoring during tumour progression and/or in response to therapy.

The role of tissue-resident and recruited tumour-promoting myeloid cells in tumour progression was a common theme. Both subtypes are present within tumours and are associated with distinct gene signatures. Ongoing studies are addressing how these differences affect various stages of tumour progression and, importantly, whether they can be exploited therapeutically.

The role of tumour-associated macrophages (TAMs) has been well characterized in recent years, with several groups showing that they are required for an efficient antitumour T cell response in mice. Aspects discussed in this conference included characterization of the signalling mechanisms involved in TAM recruitment to tumours, the dual role of TAMs as promoters and suppressors of metastasis, and the potential prognostic value of TAMs in patients receiving immune-checkpoint inhibitors.

The programme included discussions of other TME components, such as cancer-associated fibroblasts, neutrophils, natural killer cells and endothelial cells. Advances in experimental models have enabled the study of physiological states relevant to tumour progression, such as ageing, tumour dormancy and hypoxia.

In summary, an extensive degree of heterogeneity exists even within cells of the same cell subtypes present in the TME, and efforts are aimed at characterizing cell state transitions in response to tumour progression and/or therapy. Alberto Mantovani drew a comparison with pointillism and said that we can miss the big picture if we focus too much on certain details. Patient outcomes ultimately depend on the net result of a balance between complex tumour-promoting and tumour-suppressive signals within the TME. Whether these signals can be modulated therapeutically remains an active area of research. We hope to hear the results of those studies in future events.