pentex

My MIL (stage 3 lung cancer, confined to one lung, one mass) finished up 6 weeks chemo/radiation. The follow up scans show that the tumor has gone from 4.2 cm to 3 cm and that there has been no spreading.
My question is this: can the tumor start to grow again while we wait for her to be back at full strength? Can chemo kill a tumor to the point where it can't grow?

I feel like we're in a race for her life here to get her to 100% for surgery but am not even sure what happens to a tumor during chemo....