If a patient is going through cancer treatment you do need to get clearance from their oncologist for any dental treatment. During cancer treatment, especially chemo and radiation, blood cell counts can drop (white blood cells, red blood cells, and platelets). When white blood cell counts drop, their body isn’t able to fight infection (which can be fatal). Dental treatment stirs up bacteria and if the patient’s immune system is unable to fight this bacteria, it can be detrimental. Also, complete blood cell counts change throughout cancer treatment so even though you may get an okay to go forward with treatment one time, doesn’t mean the next time their blood counts are the same. Patients should have all dental treatment done before they undergo cancer treatment.
 
My dad underwent multiple rounds of radiation and chemo. I asked his oncologist about dental treatment during his treatment and he said absolutely not. Every time he had chemo, he had his complete blood cell count done. Sometimes it was so low that he couldn’t even undergo chemo that day. He wasn’t aloud to go into public places, like restaurants, grocery stores, etc. We also had to be very careful with who visited him, they had to be very healthy – no recent sickness or no recent vaccines. This is because if he would have even gotten the common cold, it could have been fatal.