As it's the recommendation of your oncologist we have to assume it's reasonable!!
If you were 48 I would say definitely not reasonable and go for the biopsy.
If you were 88 I would ask why you even bothered with an MRI.
So it's really all about your risk appetite and life expectancy.
The risks I would be considering are:
Biopsy is a procedure with a not insignificant risk.
It could be a high grade cancer that is about to metastasise.
Perhaps focus your thoughts on the above and decide which outcomes you can best live with.