Marina,
Do as Val suggests and get some supporting evidence. However beforestarting the appeal process I would suggest that you ask for a 'Reconsideration', a statement of resons, copies of all the medical evidence used and a copy of the form ( if you did not make one).
You will be able to see exactly how the decision maker reached their decision. If they sent for any medical evidence and if so was it accurate, current and did it reflect your needs ?
If it didnt then you can send in current medical evidence ( if you get any) but also explain how this disease has a monumental all consuming impact on our lives.
Detail your diagnosis ( even if you did before), how it impacts physically and emotionally, your worries, fears and recent medical history.
A reconsideration is a second bite of the cherry, before an actual appeal. Your case will be reviewd by a different decison maker who may have more understanding.
A tip.... time will be running short, get your letter planned and get any other evidence as soon as you can (GP, breast care nurse, consultant, therapist etc).
If this fails, still appeal but take your paperwork to an organisation that may be able to help you; one of the DIAL organisations, Welfare Rights or a cab.
Wishing you luck.
Julie