Have you ever taken off your nail polish only to notice a dark line on the nail running vertically down your finger? These black lines on fingernails may look like bruising or internal coloring ...

Michelle Tagliamonte, 58, was getting a manicure when she noticed the black lines on her thumb, which signaled the start of a fast-spreading cancer.

The black lines (left) on Michelle Tagliamonte's thumb were a sign of cancer.

Tagliamonte underwent an "invasive" four-hour surgery to remove the cancer — but says she's "grateful" she caught it early An Ohio mom developed black lines on her thumbnail — an early sign of ...