David. Nicely said, assuming that Bill even has cancer. "A swollen lymph node from HPV at the base of the tongue" is all he has shared about his condition. Sandy's husband is an example of how even doctors can jump the gun and why no one should start TX without a biopsy confirmation.

Back to the OP's point: Before the cancer, my cardiologist had me on Vitamin D. After the cancer, my endocrinologist also insisted I take Vitamin D. (4000 IU daily)
I have regular blood tests done that show I used to have a major deficiency but no longer do. Their recommendations are independent of any potential cancer benefits.
Charm