I'm sorry to read about the cancer diagnosis - I went through something very similar 3 years ago, in my case it was Uterine Carcinosarcoma. I had surgery, chemo & radiotherapy.
My blood sugars went haywire for about 5 days after each chemo infusion but this was partly due to the high level of steroids they gave me. My consultant told me to ignore the readings, not to panic over them and that they would settle down again quickly. They returned to my normal with a week of finishing the treatment. The hardest thing is trying to eat sensibly when you are nauseous so please make sure they give you a good supply of medication for that.