hi minty and welcome.
At my first referral they said "we think it is very likely you have cancer but we just want the biopsy results to be sure". That was based on mammograms and ultrasound. So I think it is pretty common to be 'diagnosed' subject to histology tests & biopsy for the finer details.
Incidentally my lump was 9cm - was I shocked I didn't realise it was there? Oh yes.... but it felt like normal breast tissue, and big does not necessarily mean advanced.
And:
now the lump is gone; so in principle the cancer is gone;
and I am halfway through chemo to try to ensure that it hasn't and won't spill elsewhere; then I will have rads;
...and life is good.
I feel pretty well nearly all the time.
I only have one breast, but on the other side I have a tender pretty scar that I massage and I nurture and care for; and I can feel my ribs (first time for years);
I am being treated efficiently by lovely, caring, professional people.
The future is unknown, just as it was before my diagnosis.
This treatment process will come to an end, and all its inconveniences will come to an end.
when I have something to worry about, then I will worry, and I will not worry about things I can't know about.