Cancer is generally a broad term. It describes the disease that results when cellular changes cause the uncontrolled growth and division of cells.Some types of cancer cause rapid cell growth, while others cause cells to grow and divide at a slower rate.
Certain forms of cancer result in visible growths called tumors, while others, such as leukemia, do not.
Most of the body’s cells have specific functions and fixed lifespans. While it may sound like a bad thing but cell death is part of a natural and beneficial phenomenon called apoptosis.A cell receives instructions to die so that the body can replace it with a newer cell that functions better. Cancerous cells lack the components that instruct them to stop dividing and to die.
As a result, they build up in the body, using oxygen and nutrients that would usually nourish other cells. Cancerous cells can form tumors, impair the immune system and cause other changes that prevent the body from functioning regularly.Cancerous cells may appear in one area, then spread via the lymph nodes. These are clusters of immune cells located throughout the body.
 

Symptoms

Signs and symptoms caused by cancer will vary depending on what part of the body is affected.
Some general signs and symptoms associated with, but not specific to  cancer, include:
•    Fatigue
•    Lump or area of thickening that can be felt under the skin
•    Weight changes, including unintended loss or gain
•    Skin changes, such as yellowing, darkening or redness of the skin, sores that wont heal, or changes to existing moles
•    Changes in bowel or bladder habits
•    Persistent cough or trouble breathing
•    Difficulty swallowing
•    Hoarseness
•    Persistent indigestion or discomfort after eating
•    Persistent, unexplained muscle or joint pain
•    Persistent, unexplained fevers or night sweats
•    Unexplained bleeding or bruising