Now, doctors have a better tool to diagnose the disease.
Last fall, Andrea Syglowski was diagnosed with melanoma on her right calf. She's an actress and it was a fellow actor who noticed the mole.
"And said I have a friend who had something that looked that like that and he died so you should get that checked out," she said.
Andrea's Cancer was caught early but Melanoma kills one American every hour. It's the most common cancer among people between the ages of 25 and 29 and it's often diagnosed later in men.
Dr. Hooman Khorasani is co-founder of the new melanoma institute at Mount Sinai Hospital.
He says the number of melanoma cases keeps going up- and the use of tanning beds, the thinning ozone layer, and not wearing sunscreen are all part of the problem, but melanoma can happen to anyone of any color, even in places where the sun never shines.
"They usually present under the nailbeds or on the sole of your foot," said Dr. Khorasani.
There is new technology making it easier for doctors to diagnose.
That device works with the iPhone retina display.
Andrea says she noticed that mole on her leg had been changing last summer and ignored it at first-- but hopes you will not do the same.
LINK: MELANOMA MONDAY