When dermatologists (highly specialized skin doctors) discuss precancer of the skin, they are likely talking about the actinic keratosis lesion, i.e., the main precancer that may lead to squamous-cell carcinoma. The key words regarding precancer are "may lead to," implying that the transformation into cancer does not always occur; in fact, studies indicate that about one in twenty will develop into skin cancer, which can be alarming to patients who have large numbers of precancers. There really is no known precancer of basal-cell carcinoma and in most cases, a mole, except lentigo maligna, is not a precancer to melanoma. The actinic keratosis is the precancer that may lead to squamous-cell carcinoma, a potentially deadly tumor. Treatment of precancers and squamous-cell skin cancers are discussed in separate sections of this Web site.

Precancers will not kill or harm patients. Do not be misled by material that contradicts this statement. Precancers, by definition, have not penetrated the basement membrane of the epidermis of the skin. Some doctors feel that the basement membrane is a barrier that must be overcome in order for the abnormal cells found in the precancer to have access to the bloodstream, lymph channels and the remainder of the body. The trick is knowing which precancers already have spots of transformation or will be likely to transform into squamous-cell carcinoma. The only way to know for sure is to examine a biopsy specimen. A skin biopsy, however, is limited in its ability to show that a suspected precancer is not a SCC. The limitations are due to lesion size and biopsy processing technique. To biopsy all precancers would be impractical and expensive to say the least. Clinical hints of precancerous transformation into squamous-cell cancer or a higher potential of transformation are thickening of the precancer, pain, bleeding, long-standing nature and failure to heal. Cancer cells do not thrive on air. When any scaly precancerous lesion starts to really protrude "stick" out above the skin, it may be an indication that it is also penetrating deeply into the patient's skin in the other direction. Please note the following diagram of how precancer cells grow and might be seen under the microscope.

......Precancers that have the highest potential to cause trouble if they turn into skin cancer are usually found on the lips and ears. Possibly, the skin is thinner there and tumors may have easier access to lymph channels and blood vessels. Squamous-cell cancers forming in the lip and ear have a tendency to invade the body and the lymph system and to cause significant sickness and, many times, death. Therefore, it is best to thoroughly treat precancer of the ears and lips.

......Precancers may require treatment not only because they may become cancer but also because they have become unsightly or crusted or have failed to heal. Again, possibly, about five percent or one in twenty actinic keratoses (precancers) will become squamous-cell cancer. (Many experts cite numbers between 1 in 100 and 1 in 5.) Because it may be difficult to predict which precancer will become malignant, doctors do their best to treat as many precancers as possible in order to reduce the chance of malignancy. A certain percentage of precancers may resist treatment, depending upon the depth of treatment. The precancerous cells in these cases are usually lining a hair or sweat pore and "hiding" from treatment. Following or during healing of the treated area, precancer cells may sprout from the pore in which they have been hiding. For more information on treating precancer, see Treatment of Precancers.

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