While there is a common perception that skin pigmentation is protective against skin cancer, even individuals with the most pigmented skin can still develop these conditions, said Edmonton-based dermatologist Dr. Jaggi Rao. The incidence and relative risk of specific sub-types and their presentations differ in different ethnic groups from those of Caucasians, however, he said.
Dr. Rao is a clinical professor of medicine at the University of Alberta, and is a member of the board of directors of the Canadian Association of Aesthetics Medicine (CAAM). He spoke about the incidence and presentation of skin cancer in skin of colour at the third annual Skin Spectrum Summit in Vancouver on May 27, 2017.
“Skin cancer in ethnic skin, compared to Caucasian patients, is not as common,” said Dr. Rao. “We do not see it as often [in darkly pigmented skin], but when we do see it, it often presents quite atypically. We also see that they present at a more advanced stage.”
In Caucasians, 35% to 45% of all malignant neoplasms are skin cancer, said Dr. Rao. By comparision, for Hispanics and East Asians with similar Fitzpatrick skin type, the rate is 4% to 5%. In other Asians it is 2% to 4%, and in blacks it is 1% to 2%.
However, differences in presentation, such as lesion colour, in darker skin can delay diagnosis. “Sometimes delay it to the point that it is not actually curable anymore,” he said.
As a result, it is good to have a very high index of suspicion when examining skin lesions in patients with darker skin types, he said. As well, it is important to know which types of cancers are more common in these populations, and how they present.
He spoke about each of the most common skin cancers and how they differ in patients with more pigmented skin.
Basal cell carcinoma
Basal cell carcinoma [BCC] is the most common skin cancer in all skin types, Dr. Rao said. In Caucasian skin it typically presents as waxy papules or nodules, possibly with some central ulceration, and there may be visible telangiectasia. In darker skin, that pigment may also be found in the BCC, resulting in a black, pearly appearance. In addition to the typical risk factors such as sun exposure, BCC can be associated with some genetic conditions, such as xeroderma pigmentosum.
Squamous cell carcinoma
Squamous cell carcinoma [SCC] is overall the second most common form of skin cancer, but it is the most common skin cancer in blacks, said Dr. Rao. Why that is has not been determined, but it may be due to how collagen is somewhat more reactive in these individuals.
In Caucasians, SCC like BCC is more common in sun-exposed areas. But in darker skin it is more commonly associated with scarring and areas of past inflammation, he said.
“Sometimes we see it in burns. Sometimes we will see it in areas of scarring cause by other inflammatory conditions such as lupus – discoid lupus in particular. Sometimes even warts can turn into squamous cell carcinomas,” Dr. Rao said.
The typical appearance in this population is of a sore that will not heal, often in areas with limited or no sun exposure, such as the legs. “If ever you see anything like that – a scar that is not healing – I would suggest that you biopsy it.”
The risk of metastasis for invasive SCC lesions is usually 1%-4% he said, but if the primary tumour forms on scar tissue, risk rises to 20-40%. There is also a particularly high mortality rate in perianal tumours, possibly because patients are hesitant to present them to a doctor, and so they are diagnosed quite late, Dr. Rao said.
Melanoma is the third most common skin cancer in all patients, and can be quite deadly, said Dr. Rao. While sun exposure is a risk factor in all populations, in darker skin de novo melanomas also appear in areas with little to no sun exposure. “There is a specific type of melanoma that happens in darker skinned individuals that proves to be very aggressive and sometimes fatal,” he said. “That is the acral lentiginous melanoma.” This form of cancer often appears on the palms of the hands, soles of the feet, and under the nails or in the nail apparatus.
Of the other common types of melanoma – superficial spreading melanoma, nodular melanoma, and lentigo maligna – superficial spreading is most likely to be seen in skin of colour, he said.
Cutaneous T-cell Lymphoma
Cutaneous T-cell Lymphoma is easy to diagnose in Caucasians, said Dr. Rao. It typically appears as red, slightly scaly annular or arcuate lesions in the ‘bathing suit’ distribution. However, there is a very specific clinical presentation in darker-skinned individuals that should immediately suggest biopsy if seen, he said, which is hypopigmented patches – unusual on areas not typically exposed to the sun.
“Blacks are actually twice as likely to be affected [by cutaneous T-cell lymphoma] than people who are not as dark,” said Dr. Rao. “And there are endemic areas in the world. We see it in Japan, we see it in the Caribbean, Sub-Saharan Africa.” It is also more likely to affect the elderly and children.
Prognosis is good if there is no lymph node involvement, and there are a number of avenues of treatment including topical steroids, topical nitrogen mustard, PUVA, and narrowband UVB, he said.
There is an population in Africa where these malignant vascular lesions are endemic, Dr. Rao said. They are otherwise uncommon, and are usually seen in immunosuppressed individuals. Blacks have a higher incidence of Kaposi Sarcoma than Caucasians, but Asians have a lower incidence than Caucasians. The normal violaceous hue of these may make them harder to identify on darker skin, he said.
Dermatofibrosarcoma protuberans [DFSP] are rare in most populations, but comprise 10% of all skin cancers in blacks. “The way I think of these is like a dermatofibroma, those common, collagen-dense papules, but this is the malignant version of that. So not only will it be wider, it will also be quite thick,” Dr. Rao said. This collagen relation may explain how common it is in dark skin, as collagen is more reactive in skin with more pigment, he said. DFSP is locally aggressive and has a high recurrence rate, but metastasis is rare.