There is no one today, who has not heard about the word cancer. We all know about this disease and have seen people suffering from it. Unfortunately, some people can not survive it and lose their lives to this dreadful disease. But do we really know what cancer is? Can we say that we are fully aware of this disease? I think not.Let us know what it is in order to understand this disease so that we can be prepared to face the worst if the situation arises. What is cancer? Cancer is not a word, rather it is a term which encompasses more than 100 different types of cancerous diseases. Cancer can affect just about every organ in the human body.Many people are surprised to know that cancer can affect body parts like eyes and the heart as well. Each type of cancer is unique in its own types, causes and symptoms and methods of treatment.Some types of cancers are however more common than others.