I had both these in 2013 but wasn't diabetic at the time.
On chemo you have to have steroids for 3 or 4 days at the beginning of each cycle. These will raise your levels whilst taking them. It is also difficult to know what to eat because your taste buds change and every single thing tastes like putty at certain times during each cycle. You may also be advised to eat or drink certain things to help avoid side effects, foods that we, as diabetics need to avoid, such as cranberry juice, manuka honey, ice cream and bananas. You may also experience nausea, diarrhea and/or constipation so that may affect eating habits. Then add to that the stress to the body and how that affects your levels.
It won't be easy, but my advice is to concentrate on beating cancer rather than worrying about blood sugar levels and stressing about those in addition to everything else. One thing at a time. Once the chemo is over you can then turn your mind back to diabetes.
I wish you luck with your treatment and recovery xx