Cancers (more specifically, tumors) are highly intelligent entities. Let’s start with defining a tumor; the term refers to a mass of abnormal cells that occurs when these cells acquire the ability to divide excessively. The body’s first line of defence against tumor growth, under normal conditions, is the tight control of cell growth and division. Cancer cells, however, are able to bypass this regulation and continuously grow. A second line of defense against tumor growth is our immune system. Now, this may sound strange since we primarily think of the immune system’s function being to protect the body from diseases and illnesses such as the common cold. However, the immune system and a type of immune cell called a T cell specifically are critical for early tumor detection and clearance from the body.
One way cancer cells are smart is that they know to avoid recognition by these T cells that will ultimately destroy them. They have been known to do this by purposely depleting levels of amino acids in the immediate area of the cancer cells (also called the tumor microenvironment), which prevents the T cells from dividing in the vicinity and therefore from coming near the cancer cells . Aside from amino acids, cells need fuel in the form of glucose to maintain cellular activities and drive cell growth and division. Competition for glucose between neighbouring cells can often influence the rate of cell growth. The Pearce group from Washington University recently set out to determine whether the aggressive nature of cancer cells allows them to out-compete T cells for glucose in the tumor microenvironment. This may be another possible mechanism for cancer cells to avoid destruction by T cells .
To test this, researchers grew T cells either alone or in the presence of different types of tumor cells, and measured the release of a small signaling protein (cytokine) called IFN-γ. Once a T cell encounters a cancer cell, it should release IFN-γ to recruit other cells of the immune system to aid in killing the cancer cells. The researchers however saw that when tumor cells were present, T cells released significantly less IFN-γ, which would inhibit inflammation and tumor cell clearance by the immune system. They also noticed that when they limited glucose levels, less IFN-γ was produced. This effect was reversed if glucose was added directly to the T cells, with IFN-γ being produced at high levels again. They also found that the growth rate of the tumors cells were the same in both the presence and absence of T cells.
These findings suggest that the rate that tumor cells acquire glucose not only affects their own growth and division rates, but also limits T cells access to glucose, limiting their development. In this way, cancer cells are able to reduce the effectiveness of the immune system’s antitumor response, allowing for their continued survival.
 Munn, D.H. & Mellor, A.L. 2013, "Indoleamine 2,3 dioxygenase and metabolic control of immune responses", Trends in immunology, vol. 34, no. 3, pp. 137-143.
 Chang, C.-., Qiu, J., O'Sullivan, D., Buck, M.D., Noguchi, T., Curtis, J.D., Chen, Q., Gindin, M., Gubin, M.M., Van Der Windt, G.J.W., Tonc, E., Schreiber, R.D., Pearce, E.J. & Pearce, E.L. 2015, "Metabolic Competition in the Tumor Microenvironment Is a Driver of Cancer Progression", Cell, vol. 162, no. 6, pp. 1229-1241.