could a malpractice suit be filed against multiple care providers and a hospital?

Last feb my mother went to the ER for a serious headache in which a CT scan was requested by the ER Dr. She had a ruptured anyerism. The immediate threat had been taken care of and follow up visits monitored her progress. One year later my mother was diGnosed with stagd 4 lung cancer. In getting this devestating news we also found out that last years scan had shown the cancer and was noted on that scans report. The hospital did an internal investigation and give us a summary of their findings. We were told there were multiple care providers who knew of the "spot" and never informed my mother or our family. The was no follow up testing done. The summary apologizes numerous times and hopes it comforts us to know how they will be using this incident as a training tool. What should we do?