When we talk about Cancer, Nail Cancer is a condition that does not come up often. However, Nail Cancer, also known as subungual melanoma, is a rare but serious form of skin cancer that develops under the nail, typically as a dark streak running vertically down the nail. Initially, the cancer can be brushed apart as regular (and harmless) nail issues, but over time, it can turn aggressive and terminal. Like all Cancers, early detection is extremely important, and here are 5 signs you should look out for that might otherwise go unnoticed.