Cancer is a disease resulting from genetic mutations, which can be inherited congenitally or acquired through damage to cellular DNA.

Our bodies consist of cells, each with its own specialized role. Cancer, commonly known as malignant tumors, are abnormal growths or masses that develop from organs or body parts, originating from individual cells.

Every time a cell divides and replicates, it must copy its entire DNA. DNA replication is not completely error-free, and mutations can occur during this process, governed by fundamental biological laws. External factors such as unhealthy lifestyles, radiation exposure, and viral infections can also damage the DNA of healthy cells. When this damage accumulates sufficiently, it can lead to genetic errors and mutations.

However, not every cancer cell develops into cancer. The human body produces thousands of cancer cells daily, but very few progress to become cancerous. This is due to the body's effective defense mechanisms, which often eliminate cancer cells before they can cause harm.

The majority of errors in cellular DNA replication can be corrected by the cell's own repair mechanisms. Abnormal cells that cannot be repaired are typically eliminated by the body's defense mechanisms through programmed cell death or recognition and destruction by immune cells.

During the transition from normal cells to cancerous cells, the body's immune system plays a critical policing role. However, cancer cells can sometimes evade detection by the immune system, especially when immune function is compromised or when cancer cells develop strategies to evade immune surveillance. When this occurs, cancer cells can proliferate unchecked, overpowering the body's immune defenses.

One of the key reasons cancer typically develops over a long period, often more than 10 years, is that it requires not just a single mutation but a sequence of critical mutations to occur.

Tumor growth results from the continuous division and proliferation of cells, leading to an increase in their numbers. Modern medical examination methods can detect cancer cells in the body once they have grown to a certain size (for example, a 1 cm tumor typically contains about 109 cancer cells).

For cancer cells to thrive in the body, they require a conducive internal environment. If these conditions are not favorable or suitable, the growth of cancer cells can be restricted. This highlights that the growth of cancer in patients is often attributed to subtle changes in the internal environment that occurred long ago, leading to the emergence of cancer cells. Over time, persistent adverse stimuli can further deteriorate the internal environment, making it increasingly favorable for the rapid growth of cancer cells, ultimately resulting in cancer.

How exactly does cancer cause death?

In the early stages of tumor development, cancer cells proliferate slowly, often taking several years or even over a decade to progress from a single cell to a mass with a diameter of 1 cm. However, as the tumor reaches a certain size, the cancer cells reach a critical threshold where the immune system no longer effectively controls their growth. This allows the cancer cells to rapidly metastasize and proliferate unchecked.

When a population of cancer cells reaches approximately 1 millimeter in size, the body can no longer adequately supply them with nutrients and oxygen, nor efficiently clear their metabolic waste products. To compensate for this deficiency, the cancer cells mimic nearby normal cells and draw in nutrient-rich, oxygenated blood from surrounding tissues.

When the tumor reaches a certain size, tumor cells can detach from the primary cancer tissue and travel through the bloodstream or lymphatic system to various tissues and organs in the body. This process, known as metastasis, allows cancer cells to establish new growths (tumors) in these distant organs, leading to widespread metastatic disease.

In advanced stages, nearly all types of cancer will metastasize, causing cancer cells to multiply unchecked and damage various cells and tissues throughout the body. This relentless growth can lead to a collapse of the patient's immune system, further weakening the body. New lesions may appear, resulting in complications, and ultimately, systemic organ failure can lead to the patient's death.