What many don't understand about cancers, in general, is that they send out "tentacles" (like an octopus) in search of blood supplies. That's why the clear margin thing is such as issue and clear margins don't absolutely gaurantee that the cancer is totally gone, so in advanced cancers, stage II and up RT and chemo are used as a prophylactic measure.

Most cancers, (like mine) remain asymptomatic, until they become large enough to press against other organs. So pain isn't neccessarily a cancer indicator in itself. More then likely, it's thrush, an infection or some other cause. Which is perfectly plausible considering that the immune system typically crashes post Tx.