Immune cells are the natural enemies of cancer cells. Therefore, the life of a cancer cell is essentially a continuous battle with the immune system.

Many pieces of evidence highlight the crucial role of the immune system in controlling cancer. For example, we know that the human immunodeficiency virus (HIV) attacks the immune system, particularly the critically important T cells, leaving the body without immune defenses. Unsurprisingly, people infected with HIV are 10 to even dozens of times more likely to develop cancer compared to the general population, especially cancers like Kaposi’s sarcoma, lymphoma, and cervical cancer.

Even in a healthy human body, there is a constant battle between cancer cells and the immune system, a process known scientifically as “immune editing.” This process can span years or even decades and consists of three stages:

Stage 1: Immune Elimination.
At this stage, the immune system is dominant while mutated cells are weak. Immune cells can effectively destroy mutated cancer cells. Each time a mutated cell appears, it is immediately eradicated.

Stage 2: Immune Equilibrium.
Here, the situation becomes more complicated. Cancer cells continuously emerge and evolve, and the immune system becomes increasingly strained as it works to suppress them but cannot completely eliminate them. A state of coexistence arises, where immune cells coexist with a small number of cancer cells. Some cancer cells even enter a dormant state.

Stage 3: Immune Escape.
At this stage, certain cancer cells continue to evolve, eventually leading to the immune system losing its ability to regulate them. Cancer cells may even “hijack” the immune system, turning it against the body and aiding in their own growth and metastasis. This is when cancer is clinically detected in a hospital.

Cancer cells can coexist with the immune system in a state of “immune equilibrium” for decades. At this point, your body is likely in the immune equilibrium stage. While some mutated cells may exist in your body, they are kept in check by your immune system and pose no threat to your health.

Some may doubt this: Is it really possible for cancer cells and immune cells to coexist harmoniously over the long term?
The answer is yes! The best evidence comes from cases of “transplanted cancer.”
Under normal circumstances, cancer cannot be transmitted from one person to another. However, over 100 cases of human cancer transmission have been documented in medical literature, and the vast majority are associated with organ transplants.

One particularly striking case was reported in 2018 in an American journal on transplantation. A single organ donor unknowingly transmitted advanced cancer to four recipients after her death.
Shockingly, this transmissible cancer was highly malignant, and three out of the four recipients eventually succumbed to the disease.

This was the first-ever documented case of a single donor transmitting cancer to four organ recipients simultaneously. Subsequent investigations revealed that the donor herself was unknowingly living with a highly malignant breast cancer that had already metastasized extensively to her lungs, liver, kidneys, and other organs. Neither she nor her doctors were aware of her condition.

Without a doubt, this organ donor was in the immune equilibrium stage. Although she had highly malignant cancer cells that had spread throughout her body, her immune system managed to keep them in check, preventing tumor formation. She experienced no symptoms, and even thorough medical examinations failed to detect any signs of cancer. Her immune cells and cancer cells coexisted peacefully.

However, when the cancer cells were transferred via organ transplantation into individuals with suppressed immune systems, the balance was disrupted. Cancer cells gained the upper hand, proliferating explosively and ultimately leading to cancer in the recipients.

Thus, as long as the immune system remains dominant, cancer cells are not a threat. Only when the immune system loses control do cancer cells become dangerous. Protecting your immune system is critical to preventing cancer. To reduce your cancer risk, it’s important to avoid activities that harm the immune system, such as smoking, drinking excessively, staying up late, and overexerting yourself.

Long-lived cancer patients are simply those who have successfully coexisted with cancer cells for a long, long time.