I think you should use the cream for a week, to start with.

Also, thought experiment: Suppose a person is going to live another 70 years. If undergoing some oversimplified miracle-cure treatment will cost, one way or another, 1 week of their life, what chance of "it's just a cyst" will they accept? 99.97%. So from the doctor's perspective (neglecting other risks or resources used, taking their '99.95%' probability estimate at face value, and assuming that a biopsy is some irreplaceable road to health), your condition is so likely to be benign that the procedure to surgically check spends your life at about the same rate as it saves it.