Cancer is a complex disease characterized by abnormal cell behavior. It arises when cells lose normal regulatory mechanisms, leading to uncontrolled growth and the potential to spread. Understanding these cellular characteristics helps define the disease’s fundamental nature.
Uncontrolled Growth and Division
Cancer cells exhibit unchecked proliferation, dividing continuously without the usual signals that regulate cell growth in healthy tissues. In a healthy body, cells follow an orderly process of division, growth, and death, replacing old or damaged cells. This regulated cycle ensures tissues maintain their proper size and function.
Cancer cells ignore these normal stop signals. This uncontrolled growth often results in a tumor, a lump of abnormally growing cells. Unlike benign tumors that remain localized, malignant tumors can invade surrounding healthy tissues.
The genetic material within cancer cells, specifically their DNA, becomes damaged, leading to these altered properties. Genes responsible for regulating cell division can be affected, causing an imbalance between cell proliferation and programmed cell death. This imbalance fuels the continuous production of new, abnormal cells.
Resistance to Programmed Cell Death
Normal cells have a built-in mechanism called apoptosis, or programmed cell death, which removes damaged, old, or unnecessary cells. This process ensures the body maintains balance and removes potentially harmful cells.
Cancer cells develop ways to resist this programmed cell death. They acquire changes that allow them to survive and accumulate even when abnormal or damaged, bypassing the body’s natural quality control system. This evasion means faulty cells persist and contribute to tumor growth.
Many normal cells depend on signals from growth factors or their environment to prevent apoptosis. Cancer cells often lose this dependency and can survive without these signals, aiding their survival when spreading to new locations. While normal cells undergo apoptosis after DNA damage, many cancer cells fail to do so, allowing them to continue dividing despite genetic errors.
Sustaining Nutrient Supply
Rapidly growing cancer cells have a high demand for nutrients and oxygen. To meet these needs, tumors induce the formation of new blood vessels through angiogenesis. This new vasculature serves as a dedicated supply line, delivering oxygen, glucose, and other essential molecules directly to the tumor cells.
Tumors release specific chemical signals, such as growth factors, that stimulate nearby blood vessels to sprout and grow towards the tumor mass. This process is important for the tumor’s continued expansion and survival. Without an adequate blood supply, a tumor’s growth would be limited, as cells in the center would quickly run out of oxygen and nutrients and die.
The newly formed blood vessels within a tumor are often disorganized and leaky compared to normal vessels, but they are effective enough to sustain the tumor’s rapid metabolic demands. This self-created blood supply ensures cancer cells receive continuous resources, facilitating their growth.
Spreading to Other Parts of the Body
Metastasis is the process by which cancer cells detach from the primary tumor and travel to distant parts of the body to form new tumors. This makes cancer particularly dangerous and challenging to treat, as the disease is no longer localized to one area.
Cancer cells can break away from the original tumor and enter the bloodstream or lymphatic system, the body’s transportation networks. Once in these systems, they circulate throughout the body, eventually lodging in distant organs or tissues. There, they begin to divide again, establishing secondary tumors, also known as metastatic cancers.
This spread can occur to various organs, depending on the cancer type and its original location. For instance, breast cancer might metastasize to the bones, lungs, or brain. The formation of these secondary tumors complicates treatment significantly, as the disease is no longer confined to a single, surgically removable site.
Evading the Body’s Defenses
The immune system acts as the body’s internal defense mechanism, constantly surveying for and eliminating abnormal or diseased cells. Immune cells, such as T-cells and natural killer cells, recognize and destroy cells displaying unusual markers. This surveillance helps prevent the development of many cancers.
Cancer cells develop various strategies to avoid detection and destruction by the immune system. They can alter their surface proteins, making them less recognizable by immune cells. Some cancer cells may also produce substances that suppress immune cell activity.
Certain cancer cells can even mimic normal cells, or hide their abnormal features, allowing them to escape immune surveillance. This evasion allows cancer cells to proliferate unchecked, as the body’s natural defenses are unable to mount an effective attack against them.