Wow. Great extra info. I found this Web MD article on MD's so called "throat cancer". MD Cancer WebMD Here is an excerpt.
I can vouch that it is quite possible that MD's base of tongue cancer did not have any major symptoms until it's in Stage IV. At least this article mentions HPV. Wonder if MD had his tumor tested?

[quote]
What is throat cancer?

Surprisingly, doctors don't use the term "throat cancer." Several different kinds of cancer can involve different parts of the throat and mouth.

Michael Douglas says he has a walnut-sized tumor at the base of his tongue. If that's truly where his cancer started, he likely has oropharyngeal cancer.

Oropharyngeal cancer may involve the base of the tongue, the tonsils and surrounding tissues, the soft palate, or the front and back walls of the throat.

Doctors use the term "insidious" to describe base-of-tongue tumors. That's because there is no pain sensation at the base of the tongue, so the tumors can become quite advanced before symptoms appear.[/quote]

Also glad I read thia article before I questioned his 80% figure as the doctors in this article thought that was correct
[quote]Later stages are more problematic. Douglas says his doctors have diagnosed "late stage IV" cancer.

"For the advanced stage IV cancers, it depends on the situation with the lymph nodes in the neck," Har-El says. "There is over a 60% chance of remission if it has not spread to the lymph nodes. But if it already has spread to the lymph nodes in the neck, the odds of remission are more like 40% or 30%."

Douglas says his cancer has spread to his head and neck, but that his doctors say his odds of survival are 80%.

Teknos says there's no reason to doubt this assessment.

"We think he is still in the curable category, stage IVa," he says. "Of course we don't know, but his curability could be quite acceptable."[/quote]
My doctors went with the 30 percent which was not pleasant news
Charm