Cells are the basic units of human body. They grow and divide to make new cells as the body needs them. Usually, cells die when they get too old or damaged. Then, new cells take their place.
Cancer begins when genetic changes interfere with this orderly process and cells become abnormal due to some trigger which leads to unlimited cell division. Cells start to grow uncontrollably. They secret some factors which protect them from immune system of host. These cells may form a mass called a tumor.
A tumor can be cancerous or benign. A benign tumor can grow but will not spread. A cancerous tumor is malignant, meaning it can grow and spread to other parts of the body.
They can migrate through blood or lymph through which they can reside in other parts of body where they potentially can cause damage to that tissue or organ and ultimately its functions.
They also get the capacity to invade the tissue they are lying upon.
There are more than 100 different types of cancer. Most cancers are named for the organ or type of cell in which they start.
Patients can have following symptoms:
New onset lump or swelling in any part of body
Non healing ulcer
Any new painless growth (Gradually increasing)
Weight loss with no known reason
Dry cough not going away
Sudden change in voice
Headache with nausea and vomiting
Loss of appetite with above symptoms
Change in bowel / bladder habits
Sudden loss of power of any limb or imbalance
Episodes of seizures/fits
(Disclaimer: These are the symptoms which are the most common but not specific to a cancer. They are always to be correlated clinically by a doctor and others signs and symptoms backed by investigations)