Glad the tumour's benign.
It's interesting to hear the differences in laws around the driving issue around the world. Just for interest & comparison, the UK position has an interesting compromise between medical confidentiality and the public interest. Over here, doctors are only obliged to break confidentiality and inform the authorities if there are strong grounds to believe the patient is ignoring your professional advice and continuing to drive despite a risk. Otherwise, it operates more on a vague "don't ask, don't tell" principle. You offer your professional advice for them not to drive, inform them of their legal obligation to inform the licensing authority of this and of your legal obligations to break confidentiality if you think they're driving and that's it. Unless they're daft enough to actually tell you they're continuing to drive (or you see them driving, or otherwise find out they're driving) you're not obliged to break confidentiality. Of course, if they DO drive despite your advice and don't inform the licensing authority, they're going to get well & truly hauled over the coals from an insurance and legal perspective. The law in our case protects medical staff from liability, not the patient.
Anyway, that's rather by the by. Glad the tumour's not malignant & hope it's ultra-ultra-ultra slow-growing!