Melanoma is the best-known skin cancer, being one of the most aggressive, but it is not the most widespread. Basal cell carcinoma and squamous cell carcinoma are more frequent. The different types of skin tumors originate from different cells that make up the epidermis. Melanoma develops from melanocytes, the cells responsible for the production of melanin, the substance that gives the skin its natural color and protects it from sunlight.
We talk about this topic with Dr. Riccardo Borroni, dermatologist at Humanitas.
Basal cell carcinoma, the most common cancer
Basal cell carcinomas (colloquially also known as basalomas) originate from the cells of the basal layer, the deepest layer of the epidermis. They are the most frequent cancers of all and generally occur after the age of 50, although it is increasingly common to find them in younger subjects. These tumors usually form on the skin of the face, in particular on the nose, but also on the neck and trunk: it is in fact the parts of the body most exposed to the action of sunlight that are most affected.
There are several risk factors for this tumor: phenotypic ones, with a higher risk for individuals with light skin, eyes and hair; environmental ones, with prolonged sun exposure over the years and without protection from ultraviolet radiation from the sun. It should be noted that UV radiation from tanning lamps and sun beds is also harmful. The DNA of basal cells is damaged by UV rays, triggering the origin of the carcinoma. That’s why developing a basal cell carcinoma is a “warning sign” for the development of another basaloma or other skin tumors caused by exposure to UV. The genetic predisposition to basal cell carcinoma is extremely rare, which occurs with Gorlin-Golz syndrome, characterized not only by the appearance of basal cell carcinomas in young adulthood (20-25 years), but also by skeletal malformations, brain tumors and typical point depressions to the palm of the hands and to the soles of the feet.
How are basal cell carcinomas treated?
Basal cell carcinoma develops slowly and almost never spreads to other organs. Its prognosis is favorable and the treatment of first choice is surgical, most often decisive.
In selected cases, when the tumor is superficial, it is located in places such as the face, and when the patient’s condition (including age and some drug therapies) contribute to a higher risk of complications of surgery (hemorrhage, infections), other therapeutic, non-invasive options may be considered.
For superficial basal cell carcinomas, for example, imiquimod 5% is indicated, which when applied in cream on the basaloma, activates the immune system to eliminate diseased cells; photodynamic therapy: the application of a drug (aminolevulinate) makes the cells sensitive to light, this then activates the same drug that “destroys” the cancer cells of the skin. In the rare forms of metastatic basal cell carcinoma, or when the size and anatomical location of the tumor do not allow radical surgical removal, radiotherapy or systemic therapy with vismodegib may be used.
Squamous cell carcinoma
Squamous cell carcinoma also originates from keratinocytes, which can undergo a neoplastic transformation giving rise to a malignant tumor. The clinical course of this tumor is variable, and includes non-invasive forms, and others with metastatic potential.
This form of skin cancer also develops on the regions of the skin most exposed to sunlight, but since UV rays are not the only cause, this tumor can form in any area of the skin surface and mucous membranes.
Risk factors are always linked to the light phenotype (red or blond hair, light skin, blue or green eyes); to exposure to ultraviolet radiation and to the use of tanning lamps and beds. The immune system plays an important role in the risk of occurrence and progression of squamous cell carcinoma, which is the most common cancer in people transplanted for treatment with immunosuppressive therapies. Another element of risk is contagion with Human Papilloma Virus (HPV), which in some cases can promote the onset of certain types of squamous cell carcinoma. Genetic predisposition factors include oculocutaneous albinism, pigmentose xeroderma and boiled dystrophic epidermolysis.
The treatment of choice is surgical; for in situ forms, i.e. not yet invasive (Bowen’s disease) photodynamic therapy is useful.
Useful for identifying patients at risk of developing cancer is recognizing actinic (or solar) keratoses: superficial, non-invasive precancerous lesions caused by exposure to UV rays. Over time, some actinic keratoses may develop into invasive squamous cell carcinoma if left untreated.
Actinic keratoses appear as small pink or red spots, with a rough surface, which tend to join each other; they usually arise on the face and back of the hands, or on the scalp of bald men. If lesions appear on the lower lip, this is referred to as actinic karylitis.
Isolated lesions are treated with cryotherapy or diathermocoagulation, while photodynamic therapy with aminolevulinate and topical therapy with diclofenac 3%, imiquimod 3.75% or mebated ingenol are indicated when they are extensive or confluent; different drugs that are applied locally and with different modes of action are able to intervene on the “carcinogenic field”, that is on the whole area of the skin that has been subject to the action of UV rays and that hosts those alterations not necessarily visible to the naked eye, which if left untreated can represent the first step for the development of squamous cell carcinoma.