Cancer is a disease that begins when normal, healthy cells in our body undergo changes in their DNA. These changes, called mutations, cause cells to lose their normal behavior and start growing uncontrollably. Let's explore how this transformation happens step by step.
DNA damage can occur from many sources. External factors like ultraviolet radiation from the sun, X-rays, and harmful chemicals such as those in tobacco smoke can damage our DNA. Viruses can also insert themselves into our genetic code. Additionally, as we age, our cells make more errors when copying DNA during cell division. Some people inherit damaged genes from their parents, making them more susceptible to cancer.
When DNA mutations occur in specific genes that control cell behavior, cells lose their normal regulatory mechanisms. Oncogenes, which normally promote controlled cell growth, become overactive when damaged. Tumor suppressor genes, which act as brakes to prevent excessive growth, become disabled. DNA repair genes that normally fix mutations also become damaged, allowing more errors to accumulate. This creates a cascade where cells can no longer follow the normal cycle of growth, checking for errors, dividing, and resting.
Once cells lose their normal controls, they begin dividing rapidly and uncontrollably. What starts as a single abnormal cell quickly multiplies into two, then four, then eight cells, and so on. This exponential growth forms a mass of cells called a tumor. As the tumor grows, the cancer cells continue to accumulate more mutations, making them increasingly abnormal and aggressive. The tumor may also stimulate the growth of new blood vessels to feed its rapid expansion. Tumors can be benign, meaning they stay in one place, or malignant, meaning they have the potential to invade surrounding tissues and spread to other parts of the body.
The most dangerous aspect of cancer is its ability to invade and spread. Initially, cancer cells break through the barriers that normally contain them and invade nearby healthy tissues. In advanced stages, cancer cells can enter the bloodstream or lymphatic system and travel to distant parts of the body. When these traveling cancer cells settle in new organs like the liver, lungs, or brain, they form new tumors called metastases. This process of metastasis is what makes cancer particularly dangerous and challenging to treat, as it transforms a localized disease into a systemic one affecting multiple organs throughout the body.