Doctors have long said that the body's most important defense against cancer is immune cells, which play a crucial role in defeating abnormal cancerous cells in the body. New insights into this field of research are suggesting, however, that some of those immune cells meant to fight cancer, can actually help cancer grow.

The most researched cells involved in this are macrophages, a type of white blood cell that engulfs and destroys foreign cells seen as threats to the immune system. Research studies have found that when macrophages infiltrate these tumors, they become tumor-associated macrophages (TAMs). TAMs become recruiters for cancer, helping it further invade the immune system. In a 2025 article , researchers explored TAMs central role in tumor growth. They found that tumors can release signals that train the TAMs to provide an anti-inflammatory role for the tumor.

This process also occurs in T-cells and is known as T-cell exhaustion. T-cells are white blood cells that act as one of the immune system’s primary forces in attacking tumors and diseases. However they are highly exposed to tumor antigens, which can lead to T-cell exhaustion. As a result, they stop attacking and start producing inhibitory receptors such as PD-1, which stops all activity against the tumor’s cells. This can cause cancer tumors to grow rapidly, potentially causing a sharp decline in health.

A major reason why this research is fairly new to the scientific world is due in part to the previously widely accepted functions of these cells, known to do the opposite — fight cancer. The normal function of macrophages and T-cells are to protect and calm down the immune system, rather than further attacking and damaging it.

Although cancer remains one of the most fatal diseases, greater research in areas involving cancer could be a huge driving factor for the rise in survival rates. Research done by the American Cancer Society has found that cancer death rates have declined by 34% since the 1990s. A substantial reason why this percentage has continued to go up is due to research on how T-cells work to create therapies to fight back against cancer invading the immune system.

Understanding how cancer grows is a fundamental part of improving the treatment of tumors. Cancer can manipulate the body’s built-in protection systems to instead recruit them to grow tumors. This knowledge has caused a shift in focus within cancer research to further investigate this process and better understand how it can be harnessed for therapies. This promising field of research could potentially create more treatment plans to successfully kill off cancer tumors.