Precancer is a group of congenital and acquired pathological conditions that precede the development of an oncological lesion, but do not always transform into a malignant tumor. It can be optional or obligatory. The group of precancers includes a large number of inflammatory, non-inflammatory and dystrophic diseases, malformations, age-related changes and benign neoplasia. It is diagnosed on the basis of clinical, laboratory and instrumental studies. Treatment tactics and measures to prevent malignancy are determined by the type and localization of the pathological process.
Meaning
Precancer – changes in organs and tissues, accompanied by an increase in the likelihood of developing malignant neoplasms. Their presence does not necessarily mean transformation into cancer, malignancy is observed in only 0.5-1% of patients suffering from various forms of precancer. The study of this group of diseases began in 1896, when dermatologist Dubreuil proposed to consider keratoses as pathological conditions preceding skin cancer. Subsequently, the theory of precancer became the subject of research by doctors of various specialties, which led to the formation of a whole concept that takes into account the clinical, genetic and morphological aspects of the formation of cancerous tumors.
The modern version of this concept is based on the idea that malignant neoplasia almost never occurs against the background of healthy tissues. Each type of cancer has its own precancer. In the process of transformation from healthy tissue to a malignant tumor, cells undergo certain intermediate stages, and these stages can be distinguished by studying the morphological structure of the affected area. Scientists have managed to determine the precancer for many cancers of various localization. At the same time, the precursors of other groups of oncological lesions have not yet been established in most cases. Treatment of precancer is carried out by specialists in the field of oncology, dermatology, gastroenterology, pulmonology, gynecology, mammology and other fields of medicine.
Classification
There are two types of precancers: facultative (with a low probability of malignancy) and obligate (degenerating into cancer in the absence of treatment). Specialists consider these pathological processes as two initial stages of cancer morphogenesis. The third stage is non–invasive cancer (carcinoma in situ), the fourth is early invasive cancer. The third and fourth stages are considered as the initial stages of the development of a malignant neoplasm and are not included in the group of precancerous.
Taking into account the localizations , the following types of precancers are distinguished:
- Skin precancers: Paget’s disease, Bowen’s dyskeratosis, xeroderma pigmentosa, cutaneous horn, senile keratosis, radiation dermatitis, long-term fistulas, post-traumatic and trophic ulcers, post-burn scars, skin lesions in SLE, syphilis and tuberculosis, congenital malformations and acquired skin diseases.
- Precancerous red border of the lips: dyskeratosis, papillomas.
- Precancerous oral mucosa: cracks, ulcers, leukoceratosis.
- Precancerous nasopharynx and larynx: papillomas, dyskeratoses, basal fibroid, chondroma, adenoma, contact fibroma.
- Precancerous breast: nodular and diffuse dishormonal hyperplasia.
- Precancerous female genital organs: hyperkeratosis, erosion and polyps of the cervix, endometrial hyperplasia, endometrial polyps, adenomatosis, cystic drift, some ovarian cysts.
- Precancerous gastrointestinal tract: post-burn scars of the esophagus, leukoplakia of the esophagus, gastritis, gastric ulcer, adenomatous polyps of the esophagus, stomach and intestines, ulcerative colitis, fistulas and cracks of the anus, scars of various localization.
- Precancerous liver and biliary tract: cirrhosis, gallstone disease, hepatoma.
- Pre-cancers of the urinary tract, testes and prostate: leukoplakia of the bladder mucosa, papillomas, adenomas, cryptorchidism, prostatic hyperplasia, testicular teratoid tumors, specific lesions of the testicular appendage in gonorrhea and tuberculosis.
Facultative precancers are chronic diseases and conditions with a relatively low risk of malignancy. Such pathological processes are accompanied by dystrophy and atrophy of tissues, as well as disruption of cellular regeneration processes with the formation of areas of hyperplasia and metaplasia of cells, which can subsequently become a source of malignant tumor. The group of facultative precancers includes chronic nonspecific and specific inflammatory processes, including esophagitis, atrophic gastritis, gastric ulcer, ulcerative colitis, cervical erosion and many other diseases. In addition, this group includes some developmental anomalies, age-related changes and benign neoplasia.
Obligate precancers are considered as pathological conditions that, if left untreated, sooner or later transform into cancer. The probability of malignancy in such lesions is higher than in facultative precancers. Most obligate precancers are caused by hereditary factors. Such diseases include adenomatous polyps of the stomach, Bowen’s dermatosis, pigmented xeroderma, familial polyposis of the large intestine, etc. A feature of obligate precancers is dysplasia, characterized by a change in the shape and appearance of cells (cellular atypia), a violation of the process of cell differentiation (the formation of cells of various maturity levels with a predominance of less specialized forms) and a violation of tissue architectonics (a change in the normal structure, the appearance of areas of asymmetry, atypical cell disposition, etc.).
Specialists usually distinguish three degrees of dysplasia in precancerous: mild, moderate and severe. The main criterion determining the degree of dysplasia is the level of cell atypia. The progression of dysplasia is accompanied by an increase in cellular polymorphism, an increase in nuclei, the appearance of hyperchromicity and an increase in the number of mitoses. The appearance of areas of dysplasia in precancerous does not necessarily end with the formation of a clone of malignant cells. It is possible to stabilize the process, decrease or increase the severity of pathological changes. The more pronounced the dysplasia, the higher the probability of malignancy.
Precancerous conditions
Skin precancers
Precancerous skin diseases are a widespread and well-studied group of precancerous diseases. The leading place in the list of factors provoking such pathological conditions is occupied by adverse meteorological effects, primarily excessive insolation. In addition, high humidity, wind and low ambient temperature are important. Pre–cancers of the skin can be provoked by prolonged contact with chemical carcinogens, including tar, arsenic and lubricants. Radiation dermatitis occurs when receiving a high dose of ionizing radiation. The cause of trophic ulcers are blood supply disorders. Post-traumatic ulcers can form at the site of extensive purulent wounds. Unfavorable heredity plays an important role in the development of some diseases.
The risk of keratoacanthoma malignancy is about 18%, skin horn – from 12 to 20%, post–burn skin lesions – 5-6%. The diagnosis of precancerous skin is made taking into account the data of anamnesis and external examination. If necessary, the material is taken for cytological examination. Treatment usually consists in excision of altered tissues. Surgical removal, cryodestruction, laser therapy, diathermocoagulation are possible. With some precancerous diseases, therapy of the underlying disease, bandages, skin plastic surgery, etc. are required. Prevention consists in minimizing harmful effects, compliance with safety regulations when working with chemical carcinogens, timely and adequate treatment of traumatic injuries and inflammatory skin diseases. Patients at risk should be regularly examined by a dermatologist.
Precancerous gastrointestinal tract
Precancerous gastrointestinal tract include a large number of chronic diseases of the gastrointestinal tract. The most important are atrophic gastritis, tumor-stimulating gastritis (Monetrier’s disease), gastric ulcer, adenomatous polyps of the stomach and intestines, Crohn’s disease and ulcerative colitis. The causes of precancerous development may vary. Important factors are unfavorable heredity, infection with Helicobacter pylori, eating disorders (irregular meals, eating spicy, fatty, fried) and autoimmune disorders.
The probability of malignancy of precancerous gastrointestinal tract varies significantly. With familial polyposis of the colon, malignancy is observed in 100% of cases, with large adenomatous polyps of the stomach – in 75% of cases, with Monetrier’s disease – in 8-40% of cases, with atrophic gastritis – in 13% of cases. In gastric ulcer disease, the prognosis depends on the size and location of the ulcer. Large ulcers are malignized more often than small ones. With the defeat of a large curvature (a very rare localization of the ulcer), malignant degeneration is noted in 100% of patients.
The leading role in the diagnosis is usually played by endoscopic methods of examination. During gastroscopy and colonoscopy, the doctor evaluates the size, localization and nature of the precancerous and performs an endoscopic biopsy. Treatment tactics are determined by the type of pathological process. Patients are prescribed a special diet, conservative therapy is carried out. With a high risk of malignancy, surgical excision of precancerous cells is performed. Preventive measures include compliance with the diet, timely treatment of exacerbations, correction of immune disorders, early detection of persons with hereditary predisposition, regular examinations of a gastroenterologist in combination with instrumental studies.
Precancers of the female reproductive system
In the group of precancerous diseases of the female reproductive system, specialists combine precancerous female genital organs and mammary glands. Among the risk factors for the development of precancerous diseases, researchers indicate unfavorable heredity, age-related metabolic and endocrine disorders, early onset of sexual life, multiple births and abortions, absence of childbirth, sexually transmitted diseases, some viral infections (human papillomavirus, herpes virus type 2), smoking, the use of chemical contraceptives and occupational hazards.
When diagnosing precancer, data from gynecological examination, colposcopy, hysteroscopy, pelvic ultrasound, Schiller test, cervical scraping studies, mammography, histological examination and other techniques are taken into account. Treatment may include diet, physiotherapy, hormonal drugs, antipruritic and antimicrobial agents, etc. Chemical coagulation, diathermocoagulation, radiodestruction, cryosurgery and traditional surgical techniques are used to remove various types of precancerous. Indications for surgery and the scope of intervention are determined individually, taking into account the history of the disease, the risk of malignant transformation, the patient’s age and other factors.