Cancer
Cancer is the general term for malignant tumors, which is a group of diseases
involving abnormal cell growth with the potential to invade or spread to other parts
of the body. Compare with benign tumors, infectious tumors are named for
malignant tumors. When a cell mutates in the body, it will continue to divide due to
loss of control for proliferation, eventually forming cancer. All organs in the body are
composed of cells. Cell proliferation, differentiation and apoptotic pathways allow
cells in the body to keep balance. However, if cells sustain to divide owing to loss of
control, the extra cells will form tumors. In malignant tumors, it always shows the
biological characteristics of abnormal cell differentiation and proliferation, loss of
growth control, invasiveness and metastasis. These characters are necessary for
cancer. In cancer, the biological characteristics also shows similar phenomena, such
as: 1. Cell growth and division is out of control; 2. Cancer cell can avoid apoptosis; 3.
Blood vessel construction is promoted; 4. Invasion of tissue and formation of
metastases. Therefore, cells of malignant tumors can invade and destroy adjacent
tissues and organs. Moreover, cancer cells can pass through the tumor and enter the
blood or lymphatic system, which allows cancer to form new tumors from the
original site to other parts of the body. This process is called cancer metastasis.
Cancer is a multi-factor, multi-step complex process, and its causes are also very
complicated. For example, smoking, infection, occupational exposure, environmental
pollution, unreasonable diet, and genetic factors can cause cancer. According to
previous studies, the result shows that tobacco use is the cause of about 22% of
cancer deaths, another 10% are due to obesity, poor diet, and lack of physical activity
or excessive drinking of alcohol. Other factors include certain infections, exposure to
ionizing radiation and environmental pollutants. Approximately 5–10% of cancers
are caused by inherited genetic defects from a person's parents. In addition, 15% of
cancers are caused by infections in the developing world.