Would a melanoma remain seemingly unchanged for two years ..?

No . : If you truly have a Melanoma , you and your dermatologist you would have seen changes and it would have even taken care of ! If you are at RISK individual for moles and nevi , then you should be under the care of a Dermatologist for periodic skin check looking for skin changes . Should use dun screen and stay out of the sun and avoid sun burn and avoid sun tanning booths as well .

Very rare: melanoma by definition is malignant and can be very aggressive. The chance of remaining unchanged woud be rare. Unless one is dealing with a pigmented keratosis which is benign, one would have to evaluate the path report to see if a melanoma was diagnosised or if one should be made.

Possible: It is possible for a melanoma to remain unchanged. Different melanomas grow at varying speeds. Some change vary rapidly and spread to other locations in the body, while others grow much much slower.