Metastatic breast cancer. To doctor?

My mom had breast cancer in 2010.we found it in starting stage itself we had taken treatments such as radiation,surgery and chemo.next to dat she was in regular check up wit dat doctor for every 3 months  she was normal till a year back. Since 2017 june onwards pblms like lack of sleep in nights,heavy hip pains started.whenever she told to doctor regarding d pblms during checkup for 4 to 5 times, all d times doctor didnt considered  it serious and told her like its normal only. 2 months back she got d severe back pain i.e she cant able to get up from d bed also.dat tym we had taken her to d ortho doctor and he suggested to goahead wit d mri scan.once we informed d same to our cancer treating doc he told us to take her to his hsptl.we had done d mri and pet scan der and he informed us suddenly, she  reached metastatic state within these 2 months(i.e. after d last checkup) .nothing cant do I want to have the answer for d following questions 1.is cancer spreads bcoz of doctor carelessness