Keratoacanthoma is a benign neoplasm of epidermal origin, in some cases having a tendency to malignancy. Depending on the shape of the tumor, it is accompanied by the formation of one or more nodes on the skin of the face, limbs and trunk. Neoplasms grow rapidly, but then they can spontaneously disappear, leaving behind scars. Diagnosis is based on the results of examination, biopsy and histological examination of a tissue sample. Treatment is usually surgical, in some cases it is not required due to the independent resolution of the tumor.
Keratoacanthoma (tumor–like keratosis) is a rapidly growing benign tumor of the skin that occurs under the influence of various factors of viral, physical and chemical nature. It is usually detected in older people, men develop about three times more often than women. In dermatology, it is considered a relatively safe condition, but in almost every 20th case (in 6% of patients) it transforms into squamous cell skin cancer. Due to the danger of malignant keratoacanthoma requires special supervision, in some cases surgical removal is indicated. Another reason for choosing surgical treatment tactics is to prevent the formation of rough scars that remain after self-resolution of the tumor, which is especially important in the case of the location of the neoplasm on the face.
Reliable data on the causes of the development of keratoacanthoma are currently absent, a combination of several factors is assumed. In almost half of the patients in the tumor tissues, the DNA of the human papillomavirus (most often type 25) is determined by PCR analysis. An increased incidence of keratoacanthoma is observed in smoking patients and people who are often in contact with chemical carcinogens (tar, soot, polycyclic hydrocarbons). Some researchers note that the probability of tumor formation increases under the influence of factors such as ultraviolet radiation, radiation, frequent damage and inflammation of the skin.
For some forms of keratoacanthoma (multiple or generalized), a genetic predisposition with a presumably autosomal dominant type of inheritance has been proven. Another possible cause of the development of keratoacanthoma skin is the presence of a number of diseases, especially metabolic diseases, pathology of the gastrointestinal tract and respiratory system. There are indications of the occurrence of neoplasms within the paraneoplastic syndrome (a group of disorders caused by the presence of a malignant tumor).
All of the above factors affect the sensitivity of the receptors of epithelial cells responsible for the contact “brake” of division. Failure of the normal operation of the division inhibition mechanism leads to increased proliferation of the epidermis and the formation of keratoacanthoma. This process is accompanied by the intensification of keratinization and deterioration of nutrition of epidermal tissues, which in conditions of increased proliferation increases the risk of cellular “breakdowns”. These disorders may eventually lead to the appearance of cells prone to uncontrolled infiltrative growth, characteristic of squamous cell skin cancer.
There are several clinical forms of keratoacanthoma, differing in structure, size, localization and number of foci. The reasons why the patient has exactly that, and not another kind of this benign tumor, are unknown. So far, it has been reliably established only that most cases of multiple keratoacanthoma are caused by hereditary factors – possibly mutations of the TP53 gene or other genetic defects. It was also not possible to identify the relationship between the form of the neoplasm and the probability of its malignancy – any type of tumor-like keratosis with the same risk can lead to skin cancer.
The following types of keratoacanthoma are distinguished:
- Solitary or single – the most common type, which is characterized by the development of one pathological focus up to 3-4 centimeters in size on the skin of the face or limbs.
- Giant is a form of keratoacanthoma, the peculiarity of which is the significant size of the neoplasm. Cases have been described when the tumor reached 20 centimeters.
- Keratoacanthoma with peripheral growth – unlike most types of this neoplasia, characterized mainly by central growth, increases in size, increasing along the periphery.
- Multiple keratoacanthomas – have a pronounced hereditary character, are often accompanied by other disorders, most often by a decrease in immunity and malformations of embryonic development. Some researchers suggest that the main cause of such formations is precisely a decrease in the activity of the immune system.
- Subcutaneous keratoacanthoma is a form of tumor that forms on the nail bed or roller and is characterized by particularly rapid growth at the initial stages of development.
- Mushroom–shaped keratoacanthoma is a type of neoplasia with a smooth hemispherical surface without central ulceration and with areas of increased keratinization.
- Multimodular keratoacanthoma – often reaches significant sizes, has several foci of growth and keratinization on its surface. This type of tumor must be differentiated from the multiple form, in which several adjacent nodes can merge with each other, becoming similar to a multimodular form.
- Tubero-serpiginous keratoacanthoma is a type of tumor–like keratosis, which is characterized by reduced keratinization and partial preservation of normal (but somewhat thinned) skin covering a hemispherical neoplasm.
The forms of keratocantoma have only external differences, their histological structure remains approximately the same. Different types of tumors are similar in clinical course, and the risk of developing squamous cell skin cancer is the same. Taking into account these factors, some dermatologists suggest that the probability of the appearance of a particular type of neoplasm depends on the reactivity of the patient’s body, and not on the cause of the tumor.
The first symptoms of keratoacanthoma usually appear at the age of over 40 years, but an earlier onset of the disease is also possible. A benign tumor in the process of its development goes through several stages, the cumulative duration of which is from 2 to 10 months. The first stage begins with a slight redness at the site of the future pathological focus, sometimes there is itching or tingling. After a few days, a keratoacanthoma begins to grow rapidly on the affected area, the size of which, depending on the shape, can reach 1-15 centimeters. With multiple neoplasias, the development of several foci occurs almost simultaneously. The favorite localization of multiple keratoacantha is the skin of the face, neck and extensor surfaces of the hands, less often tumors form on the trunk.
After the termination of the first stage (growth phase) in the center of the keratoacanthoma, in typical cases, ulceration filled with horny masses is formed. Sometimes there is no recess (with a mushroom shape) or several areas of ulceration are formed within one tumor (with a multimodular variety). The skin around the node is moderately inflamed and often turns red or bluish. After the cessation of active growth, a phase of stabilization of keratoacanthoma occurs, which is characterized by the absence of neoplasia growth. In this state, a benign tumor can persist for up to several months.
The third stage, the regression phase, unlike the previous ones, is not the only option for the development of keratoacanthoma. In typical cases, the tumor begins to shrink spontaneously, scarring occurs, and after a few weeks the neoplasm disappears, leaving behind an atrophic scar. At the same time, the literature describes cases of long-term existence of keratoacanthus of the skin with a recurrent course, during which the regression phase did not end, but passed into the stage of new growth. The most unfavorable outcome of the disease is the transition of a benign tumor into squamous cell skin cancer.
The diagnosis can be made by a dermatologist or oncologist. In the process of diagnosis, specialists take into account the clinical picture of the disease and the histological structure of tumor tissues established as a result of biopsy. Examination most often reveals one or more formations on the skin of the face, hands or body with sizes from 2 to 4 centimeters with a central depression filled with horny masses. When identifying less common forms, the variability of symptoms is taken into account depending on the type of neoplasia. An important factor in favor of keratoacanthoma is the characteristic dynamics of the disease (rapid development over several months with subsequent cessation of growth).
Histological examination of keratoacanthoma allows to determine the pathomorphological stage of the neoplasm development. At the first stage, the preserved basement membrane is visible under the microscope, above which there is a depression in the epidermis containing horny masses. The epithelium on the sides of the dermis is thickened, there are no changes in the dermis. At the second stage of keratoacanthoma, strands of squamous epithelium cells begin to penetrate deep into the dermis, signs of atypia may be detected in some epithelial cells. There are signs of dyskeratosis in the epidermis, pale cells in the basal layer during staining, numerous mitoses are recorded. There is a slight infiltration of neutrophils, lymphocytes and histiocytes in the dermis, but there are no signs of pronounced inflammation. Spontaneous regression is possible at the first or second pathomorphological stage of the disease.
At the third stage of keratoacanthoma, the basement membrane is destroyed, many strands consisting of squamous epithelial cells penetrate into the dermis. Sometimes the strands break away from the epidermis, as a result, epithelial islets form in the deep layers of the skin. Areas of increased keratinization are interspersed with areas of pronounced dyskeratosis. Under the base of the pathological focus of keratoacanthoma in the dermis, there is marked infiltration by various immunocompetent cells. Sometimes infiltration passes into epithelial strands or the epidermis – many dermatologists regard this sign as a precancerous condition with a high risk of squamous cell skin cancer. As a rule, spontaneous regression is impossible at this stage, treatment with the involvement of a surgeon and an oncologist is required.
Some experts recommend that patients with a primary diagnosed keratoacanthoma wait for an independent regression of the tumor, periodically performing its antiseptic treatment to prevent secondary infection. Patients should regularly visit a dermatologist until the neoplasm is completely resolved. With a high risk of malignancy, a significant size of the keratoacanthoma, or at the request of the patient, the node can be removed using traditional surgical techniques, laser surgery, cryodestruction or electrocoagulation.
Prognosis and prevention
Despite the fact that keratoacanthoma is usually resolved independently, many specialists tend to consider the prognosis for this disease as uncertain, due to the increased risk of developing skin cancer against the background of neoplasm. After tumor regression, noticeable atrophic scars remain, because of which many patients prefer to remove neoplasia without waiting for its independent resolution. Even after a successful operation, the risk of recurrence of tumor-like keratosis persists, especially often keratoacanthoma forms again after cryodestruction.