Nonmelanoma Basics
How common is nonmelanoma skin cancer?
Nonmelanoma skin cancers, basal cell carcinomas and squamous cell carcinomas, are the most common cancers in humankind. There are approximately a million basal cell carcinomas a year in the United States and, perhaps, even more. There are probably around five hundred thousand squamous cell carcinomas. So they are really ubiquitous in the American population. They are certainly more common in the Caucasian population or the fair population than they are in people of color. Within the Caucasian population, the more possible the skin has to burn or to turn red in the sun, which we call Type 1 skin, is the more likely they'll get skin cancers. However, we do see it in all people and in virtually almost ages after the age of nineteen.
What is "basal cell carcinoma"?
Basal cell carcinomas are the most common skin cancer, and accounted for approximately 1 million cases here in the United States. Basal cell carcinoma is an abnormality of the cells in terms of growth in biology out of the bottom layer of the epidermis, known as the basal layer of the epidermis. Those cells will start proliferating and growing into the dermis and start being destructive of surrounding normal skin and tissue. They have a doubling time of approximately 1½ years, so a basal cell will double in its size, more or less, every year and a half. They occur most frequently in sun-exposed areas such as the head and neck and do not metastasise. As a result they are rarely, if ever, a threat to one's life expectancy, but they are destructive and can destroy tissue that are adjacent to it, and when this occurs on the face it can be both functionally and cosmetically impairing.
What are the types of basal cell carcinoma?
Basal cell carcinoma, the most common skin cancer, can come in various subtypes. The most frequent type of basal cell carcinoma is the nodular basal cell carcinoma, which usually clinically presents as a bump or a small elevated plaque, usually with some bleeding and crusting and with some dilated blood vessels on the top of it. That is by far the most common type of basal cell carcinoma. There is a subset of basal cell carcinoma called the superficial multicentric basal cell carcinoma. Multicentric basal cell carcinoma usually occurs on the trunk, including the proximal extremities. A multicentric basal cell carcinoma is a patch of red crusting which is usually bigger than a centimetre or a quarter of an inch, and these often will occur in multiple numbers, not just one but rather two or three at a time. Another subtype of basal cell carcinoma is the pigmented basal cell carcinoma. This will appear brown, a little brown nodule that when looked at closely by an expert will differentiate itself from a normal mole or beauty mark on the skin. These are usually somewhat opalescent or glassy in their appearance. There is a group of basal cell carcinomas known as sclerotic or fibrosing basal cell carcinomas. These basal cell carcinomas are very difficult to detect. They grow in the skin rather than on the skin. They cause a scar or retraction of the skin, and are usually only identified when they are quite large. And the last subgroup of importance is the basal squamous cell carcinoma, which is a basal cell carcinoma that has some features under the microscope of a squamous cell carcinoma. Squamous basal cell carcinomas are slightly more aggressive in their growth pattern and tend to be removed with somewhat more of an aggressive nature.
What is "squamous cell carcinoma"?
Squamous cell carcinomas are the second most common type of skin cancer after basal carcinoma. Sqamous cell carcinoma is the abnormality of the growth pattern and behaviour of cells in the epidermis called the squamous cells. These cells have an opportunity to proliferate and stay either within the epidermis or go into the deeper part of the skin called the dermis. These cells can be more aggressive when the squamous cell carcinoma is large and under certain clinical circumstances, such as in radiation burns or in patients that are immunosuppressive, and when this happens these cells do have the ability, although rarely, to metastasise to local nodes.
What is "Bowen's disease"?
Squamous cell carcinoma, the second most common type of skin cancer, does present in three different subtypes of squamous cell carcinomas. The most common type of squamous cell carcinoma is invasive squamous cell carcinoma which is a crusty, oozing lesion, which is usually somewhat painful and occurs in sun exposed areas. The other two presentations are a type of red patch, which is crusting and somewhat tender only to the touch, which a squamous cell carcinoma in situ where the cells are only within the epidermis, and then there is a subtype of that type of squamous cell carcinoma known as Bowen's disease, named after Dr. Bowen who first described this lesion over a hundred years ago. Bowen's disease shows a specific pattern underneath the skin and is localised or in situ for a long period of time. Bowen's disease, in 5 to 10 percent of the cases, will become invasive and when it does so, it does tend to behave more aggressively than the regular type of squamous cell carcinoma.
Can HPV be a factor in squamous cell carcinoma?
HPV, or the virus that causes warts, is a well known cofactor, if not the primary factor, in causing squamous cell carcinoma of the cervix. In addition, there is a lesion called Bowenoid Papulosis of the penis, where it is thought that HPV may be a factor there as well in terms of transforming normal skin into superficial squamous cell carcinoma. There have been cases of squamous cell carcinoma of the skin, particularly around the fingers, where HPV has been identified as perhaps the cause of the sores. HPV may be found to be an important factor or cofactor in many squamous cell carcinomas of the skin. At this time, with our knowledge, I think it's exploding. As people are aware there's been a recent vaccine for HPV for cervical carcinoma. This may at one day be expanded to other forms of HPV induced squamous cell carcinomas as well.
