Mole of 2-3 Years removed question

Hi,

I just had a mole removed from my chest for a biopsy, approximately about 4-5mm diametre presenting with the ABCDE's of possible Melanoma. The mole first appeared I think 2-3 years ago as a symmetrical black mole, it has never itched/bled or bothered me, and I didn't think much of it then, I have a similar one on my lower leg since childhood. it began to change a month or so ago and after some research I realized it could be a risk, and saw a dermotologist for an excision and removal for biopsy.

My question is this: is it possible that it has been cancerous for years and and spreading vertically, would there not be any other symptoms if one has had it for so long? I am wondering if I erred not getting it looked at years ago, I only recently learned that one should get all new moles after 30 or so looked at, I had thought it was for only for oddly presenting moles.

Any experience or advice about would be appreciated!

cheers, mikhael