It may be a good idea but you should put on a mask as soon as you enter the patient's room. This is because the cancer patient's immune system is already low and he or she might catch the cold. However, you could inquire from the doctors at the hospital if visiting the patient while having a cold would be a good idea or not.
No! The person with cancer already has a very compromised immune system. Plus, if they're on chemo and/or radiation, they are compromised so much more. Please wait till you're better. A mild cold to you could be pneumonia to them.