Pollyj first can I say, I have had a few tests for lumps in the last maybe ten years, and all have been fine. most times they are, for everyone, so I have learned not to worry in advance.
However, I totally understand and relate to your anxiety.
A psychiatrist once paid me a home visit because of my anxiety (I think my doctor got fed up). I was only in my twenties. He told me that what I wanted was a zip on my body so that I could zip it up and down all day to check everything was ok. He was right, but there isn't one.
At 70 I have spent, wasted so much time worrying.
My mum was like this, and she has passed it to me.
Part of it is worrying about something happening to any of my family, a lot of it is worrying about pain and dying.
I practise meditation which helps me to stop thinking about the 'what ifs'. Which are usually out of proportion to reality.
And I try to come to terms with the fact that one day I will die, and there's no point in wasting my life worrying about something I can't change.
If someone had told me forty years ago that I would still be here when I was seventy, and happy (albeit with some health problems) my life would have been so much better. So much time wasted worrying.
As a Christian I am a bit ashamed to admit I feel like this, but my faith does help a lot.
However, that's not for everyone.
I do think that speaking to a counsellor would be worthwhile.