First, don't panic. The vast majority of skin cancers can be cured with a two-minute procedure in the doctor's office, as long as you catch them early. Now for the bad news: approximately half of light-skinned people will develop at least one skin cancer. There are three types:
1. Basal cell carcinoma, by far the most common and least dangerous.
2. Squamous cell carcinoma, much less common.
3. Melanoma, least common but most likely to metastasize to other sites, including the liver.
I was surprised to read in Reference 1 that there is not a strong correlation between sun exposure and melanoma, which often occurs on body sites that are not exposed to the sun. This article reports that different studies have produced different results: some show evidence for, and some show evidence against a geographic association with melanoma risk.
Basal cell carcinoma is somewhat more common at low latitudes, where there is more risk of UV exposure from sunlight. Squamous cell carcinoma has a stronger association with sunny areas. However, breast and colon cancers are less common in the sunny latitudes, so the authors of Reference 1 recommend Vitamin D supplements for anyone who has very low sun exposure.
Reference 2 reports that basal cell carcinoma (BCC) has a 1% to 2% risk of metastases if the initial tumor is greater than 3 cm in diameter. The risk increases to 50% for lesions greater than 10 cm in diameter. These are very unfortunate cases, because BCC can be easily diagnosed at a size of only a few millimeters.
My own dermatologist checks me regularly, and freezes off any pre-cancerous actinic keratoses she finds. This is a simple and relatively painless procedure. Basal cell carcinomas are often treated by primary care physicians. Options include surgery, cryotherapy, and imiquimod cream.
The appearance of skin cancer varies widely. I've looked at many photos of skin cancers, and I don't think I will ever feel confident diagnosing myself. Many benign skin conditions look similar. So don't be afraid to ask your doctor about any suspicious skin spot. Skin cancer is almost as common as dental cavities.