Stage IV and Holding

My mother is 69 yrs old. In October 2010 she had an xray done and 3 spots were detected. In December she had a PET scan that lit up two spots on one lung and one spot on another. No other cancer was found in her body. A biopsy was performed to rule out infection, but the results came back with cancer. It was staged by the surgeon as IV having spread from one lung to the other. They were just about to start a clinical trial in March, but when they did a new CAT scan they found that lone spot on one lung had shrunk, the hope at that time was that this spot was an infection (had not been previously biopsied) not cancer--that would mean Stage I. A biopsy on this spot came back as cancer. We were back where we started Stage IV and thus far no treatment. She did 5 rounds of a clinical trial from May to August, the tumors shrunk. Just had another CAT scan on September 29th and the tumors are stable no growth. All 3 tumors are less than an inch in diameter.

When she was first diagnosed Stage IV the oncologist gave her 10 months to live. She is now into her 13 month and nothing has changed, she isn't sick, does not cough, no blood, no weight loss, no difficulty breathing. It seems very strange she has Stage IV for over 1 year and she still isn't sick. I can't help but think that something is being missed. I brought up the idea of synchronous tumors with the surgeon but he dismissed the idea.

Anyone else heard of such a case? Should it be treated more aggressively or is this just wait and see what happens?