Читать книгу Fundamentals of Cancer Detection, Treatment, and Prevention - Surya K. De - Страница 16

Cancer originates at a cellular level and can occur almost anywhere in the body. Cells are the basic building blocks making up the body, with almost 37 trillion cells in an average human. Normal human cells grow and divide in an orderly process to form new cells as the body requires them. When cells grow old or become damaged, they die, and new cells take their place.

Cancer forms when normal cell processes break down. The safeguards that are characteristic of healthy cells fail, resulting in the cells becoming increasingly abnormal or out of control. Old or damaged cells survive when they should die, and new cells form when they are not required. These extra cells may divide without stopping, forming growths called tumors or cancers. The cancer cells continue to grow and make new cells, resulting in issues in the location where they began (Figure 1.1).

Of the almost 200 different diseases categorized as cancer, most form solid masses of tissue called tumors. Blood cancers, such as leukemias, normally do not form solid tumors. However, common to both tumor‐forming and non‐tumor‐forming cancers is uncontrolled, abnormal growth.

Not all tumors are cancers. There are two types of tumors: malignant and benign. Malignant tumors are dangerous, as they can spread into, or invade, nearby tissues. When these tumors grow, a few cancer cells can break away and spread to other parts of the body through the blood or lymphatic system, resulting in the development of new tumors distant from the original tumor.

Benign tumors are not as dangerous. They do not spread into, or invade, nearby tissues or organs. Benign tumors can be large or small. When removed, they usually do not come back, whereas malignant tumors do. Nonetheless, if a benign tumor is located in a sensitive place like the brain, it can still cause some problems.