"Doctor, Is this (Myelofibrosis) Cancer?   What is Cancer?"

This the first question I asked my doctor, and the question I am asked most frequently. 

His answer was, "Well cancer is a disease caused by an uncontrolled division of abnormal cells in the body so, yes, this is cancer. However, I prefer to refer to it as a serious bone marrow disorder rather than to keep referring to it as cancer ".

What cancer is:  According to the NCI  - The National Cancer institute.

Defining Cancer

Cancer is a term used for diseases in which abnormal cells divide without control and are able to invade other tissues. Cancer cells can spread to other parts of the body through the blood and lymph systems.

Cancer is not just one disease but many diseases. There are more than 100 different types of cancer. Most cancers are named for the organ or type of cell in which they start - for example, cancer that begins in the colon is called colon cancer; cancer that begins in basal cells of the skin is called basal cell carcinoma.

Cancer types can be grouped into broader categories. The main categories of cancer include:

• Carcinoma - cancer that begins in the skin or in tissues that line or cover internal organs.
• Sarcoma - cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue.
• Leukemia - cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced and enter the blood.
• Lymphoma and myeloma - cancers that begin in the cells of the immune system.
• Central nervous system cancers - cancers that begin in the tissues of the brain and spinal cord. 
• For more information on this from the NCI click here MORE  http://www.cancer.gov/cancertopics/cancerlibrary/what-is-cancer