<s>[INST] Hello doctor,My daughter has a vertical dark streak along her nail on the middle finger only. It has been there for three months now. There is no known trauma.Could I ask what you suggest we should do? It seems to be darker than before. We went to a dermatologist and they told us not to worry because it appears to be only the nail which is affected and not the skin. However, we are very worried it could be cancer. [/INST] Hello. Hope it helps. Regards. For more information consult a dermatologist online --> </s>