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Melanoma: Through Thick and Thin

Did you know that melanoma is the deadliest form of skin cancer? About 9,000 Canadians are diagnosed annually causing approximately 1,200 deaths per year (1). The father of Western medicine, Hippocrates, long ago described these potentially deadly skin lesions as “the fatal black tumour”. For millennia, there was little to no understanding of the causes and possible treatments. All of this changed in the 19th century when physicians noted the propensity of melanoma to metastasize and later how excising certain lymph glands might prevent the spread of this skin cancer (2).

The name melanoma derives from the uncontrolled proliferation of melanocytes, cells that produce pigment in both the skin and eyes. For this reason, melanomas can also be diagnosed in the eyes (ocular melanoma). Once a rare form of cancer, the worldwide incidence of melanoma continues to increase at a pace of 4-6% yearly (3). This means 325,000 new cases globally in 2020 that will rise to 510,000 cases by 2040. Like many cancers, melanoma is more common among older lives, but not always - legendary reggae singer, Bob Marley succumbed to this illness when he was only 36 years old.

Tumour prognosis

For years, the depth of invasion into the skin, layer by layer, was the most important consideration during a patient’s prognosis. Tumor penetration only to the uppermost region of the skin, the epidermis, offered the best outcomes. However, involvement of the subcutaneous tissue, the deepest skin layer was usually associated with the worst prognosis (4).

Today, after much funding and research, the thickness of the tumor (measured in millimetres) is now thought to be the most important prognostic factor. Data shows almost no danger of cancer for lesions under 0.8 millimetres. In fact, it takes about 10 sheets of paper piled on top of each other to achieve a millimetre of thickness. Microscopic analysis can also detect if there is ulceration in the lesion, the rate of tumor cell division and more.

Prevention and treatment

Family history and genetics contribute to the risk of developing melanoma. The major preventive action is managing sun exposure. A good example is the public awareness campaign in Australia and New Zealand that began in the 1980’s, encouraging the public to Slip-Slop-Slap. This mnemonic was a catchy slogan to slip on a shirt, slop on sunblock and slap on a sun hat. The effect has been largely positive, with melanoma rates decreased in younger people, though the more elderly continue to have higher melanoma rates, likely the combination of age and lack of awareness of sun-blocking in their youth (5).

Surgical removal remains the cornerstone of melanoma treatment. Sometimes a second surgery is performed to ensure the margins around the melanoma are clear of tumor cells. A pioneering technique called sentinel lymph node biopsy is now commonly used with a chemical dye to determine if the melanoma has spread, sparing the painful harvesting of multiple nodes when the sentinel node is negative and to select patients who might benefit from adjuvant therapies (6).

References

1. Canadian Cancer Society. Melanoma Skin Cancer Statistics. Cancer.ca. May 2022.

2. Alix-Panabieres, Catherine, et al. Detection of cancer metastasis: past, present and future. National Library of Medicine. February 2022.

3. Matthews, Natalie, et al. Epidemiology of Melanoma. National Library of Medicine. December 21, 2017.

4. Wikipedia. Clark’s Level. n.d.

5. Wikipedia. Slip-Slap-Slop. n.d.

6. Reintgen, D., et al. The orderly progression of melanoma nodal metastases. National Library of Medicine. December 1994.