As far as yeast being hard to eradicate it is because it is just that Yeast a small single celled Fungi and they are so resistant to so many things. They are a parasitic organism and tend to affect skin by more so muccous membrane areas and arent known to have any relation to cancer

T1NoMo Left lateral Border of Tongue. 35 at DX
Partial Glossectomy , Modified Radical Neck Dissection
All Nodes Clear... No radiation
Frey's Syndrome & Trigeminal Neuralgia as result of surgery