Cancer is a life-taking disease typically characterized by uncontrollable growth of cells. There are more than 100 types of identified cancers and all these types are classified according to the type of cells that are affected initially.
Cancer can harm the body while damaged cells start dividing beyond control to develop masses or lumps of tissue known as tumors. However, there are some exceptions, such as leukemia – a type of blood cancer that prohibits normal function of blood by causing abnormal division of cells in blood stream.
Tumors start growing and interfering with the functions of the body affecting the nervous circulatory and digestive systems and they may also release hormones to alter the functions of the body. There are tumors that may remain in one spot demonstrating limited or no growth and are considered benign, or noncancerous.
There are some tumors that are more serious, typically malignant, when there are two things present: 
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cancerous cells manage to pass throughout the body with the use of lymph and blood systems thus destroying most of the healthy tissues through a process known as invasion The cell starts dividing and growing, thus forming new blood vessels for feeding itself in the process called angiogenesis.
When a classic tumor starts spreading successfully, to other parts of the body, growing rapidly and invading healthy tissues to destroy them, it is metastasized. The process is known as metastatic which results in a serious condition often difficult to cure.
Why and how cancer cells spread, has been a common cause of concern. According to the reports of Nature Communications released in October 2012, scientists reported that they have successfully discovered a vital clue that suggests how cancer cells start spreading.
The adhesion properties (stickiness) of the cells are responsible in some ways. There are some molecular interactions between the cells and scaffolding that will hold them right in lace and make them unstuck to the site of tumor; they are gradually dislodged and they move to reattach themselves at another site. Researchers hold that this discovery has been significant as cancer mortality is primarily attributed to the metastatic tumors – the ones that start growing from cells having traveled from the original site to other parts of the body. Only about 10 percent of all deaths caused by cancer are due to the primary stage of tumors.
Cancer, ultimately, is the result of cells growing out of control and that don’t die. Normal cells found in the body start following a regular cycle – growth, division, and eventual death. Apoptosis is the process of programmed death of cells; when the process breaks down, or fails cancer starts forming.
Unlike the normal or regular cells, cancer cells don’t experience a programmatic death but rather grows consistently and divides. This causes a mass of uncontrollable and abnormal cells that start growing out of control. There are many other factors responsible for causing cancer, such as genes and DNA carcinogens and various other medical factors.