Melanoma Actually, Part 2 (of 3)
What is a Pre-Melanoma?
You would think that dermatopathologists know what a pre-melanoma is, but actually we're not sure.
People, usually white people, have screening exams to check for moles that look atypical. Sometimes these moles that look atypical to the doctor are diagnosed as atypical nevi (sometimes called dysplastic nevi). But, these atypical moles are not believed to have the potential to develop into melanoma.
So why are atypical moles removed? Because atypical nevi mimic melanoma.
Atypical moles mimic melanoma in the clinic. A dermatologist is not sure if it is melanoma or not. It is normal to biopsy moles that are not melanoma. In our clinic, the typical rate to diagnose a melanoma is about 15-20 worrisome moles per 1 melanoma. For every 15-20 worrisome moles that a dermatologist biopsies, they can expect to find 1 melanoma. For doctors who don't specialize in skin, this number will be higher.
Atypical moles mimic melanoma under the microscope. Even under the microscope the nature of any melanocytic lesion is difficult to determine. Just like in the clinic, under the microscope we are diagnosing how much these nevi mimic melanoma. We call moles atypical and grade them into mild, moderate or severe but this grading is only to convey how much they look like melanoma. We are not grading their precancerous potential.
The fact that these atypical moles are not thought to develop into melanoma is not well understood. I am fairly sure this is not understood by patients and also perhaps some providers.
It's not that patients are stupid! This is not the way screening tests are supposed to work. From the John's Hopkins website:
A screening test is done to detect potential health disorders or diseases in people who do not have any symptoms of disease. The goal is early detection.
A screening test is meant to identify disease before it happens. Take for example a colonoscopy. Gastroenterologists visually examine and remove suspicious growths from inside your large bowel. A polyp removed during a colonoscopy will absolutely grow into a cancer if left alone*.
But the same is not true for an atypical mole. For atypical melanocytic lesions the relationship is more like this:
Atypical nevus ->->-> ???
???? ->->-> Melanoma
When melanoma is obvious, it is obvious. These cells are large, disordered, and pigmented. They are different from one another. Most eye catching is their prominent nucleolus (the dark dot in the middle of the nucleus), the cellular factory working hard in protein assembly.
If you're wondering at this point why the heck you submit to a naked total body skin exam and biopsies, there are very good reasons to do so:
Skin screening examinations are helpful to prevent a growing melanoma; if melanoma grows more it has the potential to invade deeper and is likelier to spread. When caught early, the risk of spread can be reduced and treatment made more effective.
Skin screening exams that identify atypical moles place you in a higher risk category. Atypical moles are markers for melanoma risk. Having an atypical or dysplastic mole diagnosed doesn’t mean it will grow into cancer – it means that you are at a higher risk for getting a melanoma elsewhere. Once you have an atypical mole, like I have, you should be checked regularly because you are likelier to develop a melanoma.
What would a true Pre-Melanoma look like? Occasionally we'll see small lesions - perhaps confined to the junction, or with a limited growth pattern. These lesions could harbor molecular alterations that would indicate they are on the path to melanoma. I'll discuss this difficulty of melanoma diagnosis in the next, third, post on melanoma.
*We know the molecular pathway that leads to colon cancer; mutations begin in adenomas and accumulate along a predictable, worsening course culminating in cancer. The early mutations accumulate which is what allows the cells to become cancerous. This is what makes an adenoma a precancer. Unfortunately we have not been able to identify a similar pathway for melanoma; some of the same mutations we have seen are present in both nevi and melanomas, so we can't distinguish between them based on these markers.