Losing my Mam

Hi, I lost my mam to secondary breast cancer that spread to the bones last week, my mam was 54, I feel completely lost and robbed like a lot of other people, we had a lovely 3 week holiday in Rhodes and returned home on the 5th of September, mam felt a little poorly on holiday but nothing too bad, two days after holiday mam got rushed to hospital because her kidneys were failing, after numerous scans we were told mams cancer had returned and this couldn't be cured but could be managed for a  of years, 4 weeks later  mam died, we are all in utter shock, how could this be missed previously? After 30 doctors appointments with multiple problems and various MRIs and cancer checks all proving negative, how was it not found? I just can't get my head around it, i feel so let down by everything.