Hi…I just joined today because I was diagnosed with subungual melanoma. I had the same experience.. noticed a slight streak on the left side of Biggie.thought it was some dirt that could come off. Put on a nail varnish,removed 2 weeks later to find the streak has grown downwards and dark discoloration covering 1/3 of the lower nail. Did a biopsy immediately n diagnosed with SM. Pending surgery. I hope you get yours seen to.