I don't understand

I have just got off the phone with my friend Too. She rang to tell me about a friend of ours Wren who, 4 weeks ago felt her leg aching. A few days ago the ache turned into swelling and she was sent off to her local hospital for investigation of a possible DVT.

They found no indication of deep vein thr0mbosis.

Instead, they found that Wren has metastatic disease saturating her whole body. They think that it started in her lungs and spread rapidly.

She is in a hospice now and her husband told Too that she is expected to live for a few days, a few weeks at the outside.

Wren is 46 and has two young sons. She stopped smoking 25 years ago, after having smoked for a couple of years.

She didn't feel unwell apart from the recent leg pain.

I don't understand how this could happen so quickly. How could it have started in her lungs and she not feel anything amiss? Why wasn't she allowed some symptoms so that she could be investigated and treated from an early stage and so maybe have more time with her boys?

How could she be well one day and dying the next?

I don't understand.