Precancer

What is Precancer?
A number of abnormal but relatively harmless skin growths constitute the early warning signs of skin cancer. These may be precancerous lesions, benign tumors that mask or mimic more serious ones, or malignant tumors that are at the moment just on the topmost layer of the skin. They are important to recognize, because they are a warning sign of potential skin cancer.
Precancerous Growths
Skin in a precancerous state is abnormal but not malignant. The term "precancerous" is used because these abnormal areas of skin are more likely to turn malignant than healthy skin. Precancerous growths are visible to the naked eye, and they look different from normal cells when they are examined under a microscope.
What is Early Cancer?
When malignant changes occur to the skin, but haven't spread beyond the top layer of the skin, they are called early cancers, or cancers in situ. A barrier called the basement membrane helps delay invasion by malignant cells deeper into the skin.
source-The Skin Cancer Foundation