There are no circumstances where skin cancer will “metastasize into something else”. Cancers don’t do that. Even e.g. lung cancer doesn’t “turn into” something else. If it eventually invades, say, someone’s liver, it’s still lung cancer, just growing in the liver. And is treated using the meds and techniques applicable to lung cancer, not liver cancer.
As to skin cancers, there are several “pre-cancerous” states that are safe, but easier to remove early than let possibly develop into full cancer. I get a 2 or 3 dozen of these per year. Generally treated by freezing with liquid nitrogen spray when they’re just a couple millimeters across.
True skin cancer comes in 3 varieties: Basal cell, squamous cell, and melanoma. Which are respectively cancer of the base of the skin, of the upper layer of living skin, and of the pigmentation cells. There is no way for one version to “turn into” another. In terms of likelihood in the population, it’s about 70% basal, 25% squamous, and <5% melanoma.
Each occurrence on your body is ab initio. BUT: if you’re genetically disposed to them and/or have chronic heavy sun exposure / sunburn in your history, getting one is decent assurance that you’ll have more as your life goes on. But each is a separate fresh occurrence.
Basal cell carcinoma (“BCC”) is by far the most common. Slow moving, and tends to spread laterally, leaving persistent reddish “not quite right” looking areas across the top surface of the skin. It’s sorta like crabgrass, but with shallow horizontal roots. It has essentially zero chance of metastasis anywhere. I get about 5-7 per year. They’re treated either by scraping the surface lesion off, burning it off, or undercutting it with surgery and stitches. The bigger the lesion, the farther down that treatment list they go.
Left untreated for decades, you’d end up with a big reddish patch that oozes and by then it’s hard to find a big enough piece of healthy skin to graft over all the diseased skin they’d have to remove. But easy peasy to remove when they’re <~1-2cm.
Squamous cell is carcinoma (“SCC”) is similar from the patient’s POV. There’s no good way to tell BCC from SCC by eye. One significant difference is that it likes to burrow downwards as well as laterally. So crabgrass with deep roots. The danger there is the tendency to deep roots means that, if left untreated for multiple years, surgical removal involves a lot more than a couple millimeters of skin depth. Now they’re having to cut into your meat; people lose (sometimes large) hunks of noses and ears & lips that way. If they neglect it enough decades. The deep root effect also means one area can seed other areas within a couple centimeters of itself.
Mohs’ surgery is the common approach here precisely to ensure they get at any deep roots, rather than just removing the visible top part & leaving the roots to regrown a crown of leaves. If left alone long enough, those deep roots might metastasize elsewhere with severe to fatal consequences like any metastatic tumor. But we’re talking a decade+ of neglect of a visually obvious problem.
I get 1-2 SCC’s per year. Get them removed while they’re still small and there’s really no appreciable danger above the background population. But they are a warning that ongoing surveillance by a dermo should be part of your medical maintenance process at least annually.
Then there’s melanoma. A whole different kettle of fish which if untreated for even a year has a decent likelihood of distant metastases with often fatal consequences. Easy enough to treat with bigger Moh’s surgery & very occasionally local radiation, provided its still small and not yet spread. If spread is suspected or confirmed, now it’s time for chemo, etc. Uggh. Don’t get that kind.
And that’s your crash course in dermatology.
Actually, as I was doing it, I realized it’s what I’ll be doing on the boat if we do some long-range traveling.
