If left untreated, would nodular melanoma continue to grow in 2.5 years? is 3.5mm and hasn't grown.

??: Not sure i understand. Is it truly melanoma? Why then is it not out? If you are not sure but have any lesion that looks funky, please have your doc take a look at it. Don't mess around with a melanoma, they can be nasty dudes.

Likely : Melana can grow radially (outward) or vertically (in depth), which may not be as noticeable. Please see a dermatologist soon, who can help make an accurate diagnosis and initiate proper treatment.

Why are you waiting?: Melanomas grow and eventually metastasize. If you have a known melanoma it should be surgically removed as soon as possible with appropriate margins. At that depth, a sentinel lymph node biopsy is also advised. See a dermatologist or plastic surgeon as soon as you can.