D-in-L,
My sister has been on and off chemo for several years for a very aggressive form of breast cancer. It first showed up in her neck and when the dr. went to remove the lymph nodes it was found to be extending down into the back of the chest wall. It had invaded her spine and was so far back that a normal mamogram would not have revealed it. The treatments have been effective in containing the cancer.
I hope that your mother-in-law has a good recovery and all cancer is eliminated.
Malka