1. Introduction

Precancerous diseases (syn.: precancer) – diseases and pathological processes against which the development of malignant tumors is possible [2]. Studying the precancerous process, scientists sought to clarify when the risk of a tumor is high, and when unlikely. As a result, a division of the observed changes to background and actually precancerous: facultative and obligate precancer. There are two types of precancer: facultative (with low probability of malignancy) and obligate (reborn to cancer if left untreated). Facultative precancer is a chronic disease and a condition with relatively low risk of malignancy. Such pathological processes are accompanied by dystrophy and atrophy of tissues, as well as a violation of the processes of cellular regeneration with the formation of areas of hyperplasia and metaplasia of cells, which subsequently can become a source of malignancy. Development of cancer from facultative precancer is observed in 5–10% of cases. Obligate precancer is considered as pathological a condition that, if left untreated, sooner or later turns into cancer. The likelihood of malignancy in such of lesions is higher than that of facultative precancer. Majority obligate precancers due to hereditary factors. These diseases include adenomatous polyps. stomach, Bowen's disease, xeroderma pigmentosum, familial polyposis of the large intestine, etc. A feature of the obligate precancer is a dysplasia characterized by a change the shape and appearance of cells (cellular atypia), a violation of the process of cell differentiation (the formation of cells different levels of maturity with a predominance of less specialized forms) and a violation of the architectonics of tissues (a change in the normal structure, the appearance of areas of asymmetry, atypical cell arrangement, etc.). Obligate precancer turns into cancer in 20–30% of cases.

Background diseases (ulcers, cracks, scars) precede the development of cancer. These diseases may causeproliferation of epithelial cells as a result of dystrophic and inflammatory changes in them with subsequent potential for cancer development [3]. In the presence of background cancer develops in 2–3% of cases.

2. Object of Research

Taking into account the urgency of the problem, the object of our research was to study the content of human papillomavirus in precancerous processes in the oral mucosa, to improve early detection of precancerous processes, and to apply cytological examination of smears from the oral mucosa to determine the human papillomavirus in clinical practice.

3. Material and Methods of Research

The annual incidence of squamous cell carcinoma in the United States was approximately 40000 cases, in Europe - 60000 cases, in Russia - 60000 [9].The highest incidence of cancer of the oral mucosa was observed in India, 70%. In the Republic of Belarus 717 newly diagnosed cases of cancer of the oral mucosa were registered in 2006, and in 2007 there were 707 patients and it was 735 in 2008. Cancer of the oral mucosa ranks 6 – 9th in prevalence among malignant tumors in the world [10].

The standardized indicators of the incidence of oral cancer are: Uzbekistan - 1.3, Turkmenistan - 1.1, Kyrgyzstan - 1.1, Tajikistan - 1.0, Kazakhstan - 0, 9, Russia - 0.9, Ukraine - 0.9, Belarus - 0.4 by country per 100,000 population. Cancer of the lower lip is recorded relatively more often in the southern regions of Kazakhstan and in some regions of Uzbekistan, which is associated with the bad habit of putting "NAS" (a mixture of tobacco with ash, lime and other substances) between the lower lip and the gum [11].

The onset of cancer of the oral mucosa is facilitated by bad habits: smoking tobacco, drinking alcohol, occupational hazards (in contact with oil distillation products, heavy metal salts), impaired oral hygiene and poor oral hygiene, chronic injuries (poorly installed dentures, destroyed tooth crown, sharp edge of the filling), they are responsible for the occurrence of 80% of cases of cancer of oral mucosa, and with their synergistic effect, the risk increases by 100 times [12].

Precancerous lesions, according to literature sources, account for 15.2-84.9% of all diseases of the oral mucosa18. According to NN Petrov, precancer is dystrophic, persistent, but not persistent proliferates that have not yet become a tumor; thus, precancer is a dynamic concept, not a static one. Since precancer is an unstable pathological form, it does not have clinical symptoms inherent only to it and reflects the clinic of the previous condition. At certain stages of its development, the process is reversible, and timely and rational treatment of precancer prevents the development of a malignant tumor [13].

Vitamin A deficiency increases the risk of developing cancer of the oral cavity and oropharynx. The relationship between the Herpes simplex type I virus and the human papilloma virus in the development of the tumor process of the oral cavity and oropharynx has been revealed. In 30% of cases, cancer of the oral cavity and oropharynx develops against the background of leukoplakia, erythroplakia and dysplasia [14].

The defeat of the mucous membrane can manifest itself in the form of various cracks, nodules, non-healing ulcers, seals, papillary formations that tend to grow. The most common is ulcerative form, in which rapid growth is observed in 50% of cases22. The frequent addition of a secondary infection lubricates the clinical picture and can lead to a misdiagnosis. At the same time, the tumor continues to grow, hypersalivation appears, a putrid smell and pain join. In the advanced period, the pains acquire a diffuse character and radiate to different parts of the head and neck. The separation of saliva is enhanced, which is associated with severe irritation of the mucous membrane [15].

The period of neglect is characterized by active tumor growth, further spread and damage to adjacent anatomical structures. The question of the choice of methods for diagnosing early forms of cancer of the oral cavity and oropharynx remains open. Especially difficult is the diagnosis of precancerous diseases, carcinoma in situ, stage I cancer of the oral mucosa and oropharynx. Diagnostic difficulties, despite the fact that the oral cavity is well accessible for examination, are associated with the fact that clinical manifestations of complications often occur after a certain period of time after chemical and radiation therapy and their manifestation can be very diverse [16].

The increase in morbidity, the defeat of people of working age, a high percentage of relapses indicate numerous problems in the diagnosis and treatment of these diseases. The presence of a large number of publications considering the histogenesis of precancerous lesions of the oral mucosa and lip introduces terminological confusion and creates problems in the classification of these pathological processes. Some authors focus only on leukoplakia [17].

According to some data, 61.7% of tumors of the oral cavity are detected in the late stages (ІІІ- ІѴ). Such a late diagnosis, as a rule, presupposes treatment in the form of very traumatic surgical interventions, the results of which, nevertheless, remain unsatisfactory, the incidence and mortality from malignant neoplasms of oral mucosa are characterized by a steady upward trend. At the same time, the issues of epidemiology are no less important, since without a clear idea of the prevalence of the process, the stages, the histological affiliation of a particular tumor, it is impossible to solve problems such as prevention and early detection of malignant neoplasms. That is, an effective tumor prevention system is unthinkable without a well-established oncological statistics service, which is one of the mandatory components in the complex of anti-cancer measures. Considering that the oral mucosa is most susceptible to the action of exogenous carcinogens, the special role of the environmental situation in the development of malignant neoplasms should be noted [18].

Therefore, early diagnosis with the use of screening methods for the active detection of precancerous diseases of the oral mucosa and early stages of asymptomatic cancer is of particular importance. To date there are no studies on the analysis of clinical epidemiology of tumors and pretumor processes of oral mucosa in Uzbekistan [19].

According to literary sources, precancerous lesions account for 15.2-84.9% of all diseases of the oral mucosa. Without a doubt, precancerous conditions in the development of cancer in the oral mucosa and on the lips are of particular importance. Bad habits (smoking, drinking alcohol, spicy and bitter dishes), tobacco use in Central Asia, chewing betel leaves, bad oral hygiene, chemical, mechanical, thermal effects, occupational hazards, tooth crown, edges, chronic damage to the prosthesis, the presence of various metals, fillings and prostheses from amalgam are important in their genesis [20].A virus rarely found in the oral mucosa, probably due to saliva clearance [13,14,18]. On the mucosa more than 200 HPV genotypes have been found in the oral mucosa [16]. HPV infection of the oral mucosa can lead to benign or malignant disease. The role of HPV independent risk factor in oral carcinogenesis has been well studied in literature [20]. HPV positivity is claimed to outperform traditional predictive indicators such as tumor grade and histological subtype [11,19]. According to the WHO classification, squamous cell papilloma oral cavity is a benign exophytic tumor. There are two types: isolated (single) in adults and repeatedly recurring in children. The color of the lesion changes depending on the level keratinization and vascularization [15]. Squamous papilloma of the oral cavity is considered as a harmless lesion that is not is neither transmissive nor threatening [9,11]. The location and size of oral papilloma may be used as risk factors for malignant transformation [11,17]. However, those papillomas that are present on gingiva are associated with a higher risk of malignant transformation. In addition, the size of the papilloma also correlates with the risk of malignancy; for example, if the papilloma is larger than 10 mm, the risk increases [16]. Alcohol and tobacco are considered major risk factors for cancer of the oral cavity, although other authors report an increase in the incidence of oral cancer mouth in patients who do not drink alcohol or smoke [6,8,11] benign, potentially malignant, or frankly malignant. The benign lesions are exophytic, sessile, or pedunculated, with a smooth or “cauliflower-like” white or pink surfaceMaterial for molecular biological studies were tissue samples of leukoplakia and lichen planus of the oral cavity, taken from patients during the examination. Virus DNA was isolated from the tissue homogenate using a commercial MagNaPureCompactNucleicAcidIsolationKit I-LargeVolume reagent kit on a MagNaPureCompact instrument (Roche, Switzerland). (QIAGEN, Germany). Human papillomavirus DNA of high carcinogenic risk (HPV HPV) types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59 and HPV low carcinogenic risk (HPV HPV) types 6 and 11, herpes simplex virus 1, 2 types (HSV type 1,2), cytomegalovirus (CMV), Epstein-Barr virus (EBV) and human herpes virus type 6 (HPV type 6).

We also used commercial reagent kits manufactured by Interlabservice LLC (Moscow): AmpliSens HPV HRC genotype-FL, AmpliSens HPV 6/11-FL, AmpliSens HSV1,2-FL, AmpliSens EBV/CMV/HHV6-screen -FL.

4. The Results of the Study

Relationship between precancers of the oral cavity and viral infection, namely, infection with the human papillomavirus in the majority (73.3%) of patients. At the same time, EBV was detected in all patients with metastases. Thus, with N1 out of 8 patients, 6 EBV was detected, and 2 had a com-bination of EBV with CMV and EBV with HSV types 1.2, while with N2, all had EBV. The prevalence of the tumor process corresponding to T4 occurred in 12 patients, of which 4 had EBV, 2 had EBV with CMV, 2 had EBV with HHV type 6 and 4 had EBV with CMV, HHV type 6. In the future, even after special treatment, 31.8% of patients in-fected with EBV had regional metastases and 13.65% had relapses. Human papillomavirus was detected in 6 cases, in this group of patients there are no relapses and metastases. These results are consistent with the literature data [6,7] that HPV-associated oral precancers respond better to radi-ation and chemotherapy, have a more favorable course and prognosis compared to HPV-negative patients. The re-cruitment of clinical material continues.

In the advanced period, the pains acquire a diffuse character and radiate to different parts of the head and neck. The separation of saliva is enhanced, which is associated with severe irritation of the mucous membrane. The period of neglect is characterized by active tumor growth, further spread and damage to adjacent anatomical structures. There are clinical features of the course of oral cancer in certain locations. For example, tongue cancer often occurs in the lateral region (its average third is up to 70% of cases) and the root (20-40%). Patients often independently discover a pathological focus, especially located in the anterior areas. The appearance of soreness, speech disorders, swallowing and difficulty in movement are also common symptoms. Palpation of this zone is especially indicative. Small ulcerations often have large underlying infiltrates [24].

Tumors of the tongue are characterized by early metastasis. Often, the first symptom of cancer in the distal tongue is an enlarged lymph node in the neck. With this problem, patients turn not to an oncologist, but to a general surgeon or therapist [25].

Metastasis in oral cancer to regional lymph nodes is associated with rich vascularization and often high aggressiveness of malignant tumors of the oral cavity and pharynx and reaches a frequency of up to 70%. For example, in cancer of the lateral surfaces (middle third) and the tip of the tongue, secondary foci of tumor growth are found in the submandibular, middle and deep cervical lymph nodes. The frequency of metastasis is 35%. Cancer of the distal parts of the tongue gives not only early metastases, but also frequent in almost 75% of cases [26].

With the development of a tumor on the mucous membrane of the cheeks, the floor of the oral cavity or the alveolar processes of the lower jaw, metastasis occurs in the submandibular lymph nodes. Submental lymph nodes are rarely affected by metastases when tumors are located in the anterior parts of the above organs. Cancers of the posterior oral cavity often metastasize to the middle and upper jugular lymph nodes. In cancer of the mucous membrane of the palatine surface of the alveolar processes of the upper jaw, metastases are found in the retropharyngeal lymph nodes, which are inaccessible for palpation and surgical removal. With cancerous tumors of the oral cavity, damage to any lymph nodes in the neck is possible. Supraclavicular lymph nodes are least often affected [27].

In addition, it is required to obtain sufficiently substantiated data before surgery, which would make it possible to more accurately predict the degree of extracapsular tumor prevalence and timely prescribe more aggressive therapy for patients at risk [28].Extracapsular spread (ECS) and metastasis are independent prognostic signs for squamous cell cancers of the head and neck, including oral cancer. Also, they reflect the aggressiveness of the tumor, which is associated with the possibility of local recurrence, the appearance of distant metastases and, as a consequence, an unfavorable outcome [29].

Therefore, genetic criteria have been proposed to assess the prognosis of the tumor process and metastases. In particular, in the work of Japanese scientists (S Miсhikawa et al., 2011), a relationship was revealed between the prevalence of the tumor process, metastasis and the number of EGRF (epidermal growth receptor factor) aberrations in the primary tumor. The researchers' conclusions are rather cautious, as activating mutations leading to abnormal changes in the epidermal growth factor receptor may indicate general genetic instability in the tumor. But they make it possible to use genetic laboratory instruments for these purposes. The authors propose to use the prevalence of the tumor process as an independent prognostic factor, relying on the presence of a large number of EGRF aberrations in tumours [30].

The five-year survival rate for local recurrence was also analysed. Wenzel conducted a similar study in 2004 and obtained almost the same data on patient survival, which correlates with many previous studies. The spread of the tumor, metastasis to regional lymph nodes, as well as distant metastases complicate the prognosis and shorten the survival time of patients [31].

Gebhart found a fairly frequent manifestation of the genomic imbalance in the form of an increase in 7p12, but no significant effect on the degree and prevalence of the tumor process was observed. However, the average survival in the presence of a tumor without an increase in 7p was clearly higher than with an increase in this indicator. In the affected regional lymph nodes, the 7p allelic imbalance was found with a higher frequency. Also, relapse occurred more often (63%) in cases of tumors of the 7p12-positive group, versus 25% without changes in 7p [32].

Work in the direction of studying the genetic control of metastasis was started in our country back in 1990 by a group of scientists led by EM Lukanidin at the Institute of Gene Biology. As a result of many years of research, the identified mts-1 gene, which encodes the protein metastasin-1 (mts-1). When mts-1 gene expression was suppressed, there only isolated foci of metastasis were observed in the lungs of mice. This approach was the first attempt to link the features of the clinical course of the disease with the results of molecular genetic studies. The clinical manifestations of tumor growth become noticeable much later than the first oncogenic mutations. The study of early molecular genetic changes using the example of the transformation of benign pleomorphic adenoma of the salivary glands is of practical interest [33].

Thus, the features of the clinical manifestation of oral cancer: asymptomatic course in the initial stage, the addition of a secondary infection, difficult differential diagnosis, along with late referral of patients to the appropriate specialist, lead to the diagnosis of this process already at later stages. At the same time, there are enough data in the literature proving the influence of molecular genetic factors on the occurrence, metastasis and on the features of the clinical course of cancer, the further study of which at the modern level of science becomes a practical [34-35].

Bowen's disease. It is localized more often in the parts of the oropharynx (palatine arches, soft palate, tongue root). The retromolar areas and the red border of the lips may be affected. Elements of the lesion are manifested in the form of erythema, papules, erosions. At the beginning, there is a maculo-nodular lesion with a diameter of 1.0 cm or more. The surface of the site is hyperemic, smooth or velvety with small papillary growths. Slight flaking and itching are possible. Then the lesion slightly sinks, erosion appears on its surface. Histologically, this disease is referred to as "cancer in situ" [36].

Erythroplakia Keira. It was first described in 1921. On the mucous membrane of the lips and cheeks, sharply outlined bright red foci appear with a barely noticeable compaction at the base. The lesions rise slightly above the mucosal surface. The surface of the lesions is smooth, hyperemic, velvety. Gradually, ulcerations appear on the surface of the lesion and 100% degeneration into cancer with metastasis to regional lymph nodes [36].

Warty precancer. Exophytic formation of the mucous membrane, after scraping the scales from which a large-tuberous surface with significant or moderate keratinization is exposed, loop-shaped and atypical vessels can be observed [36].

Limited precancerous hyperkeratosis. Gray-yellow focus of "calcification" with small shiny scales. The relief is shallow, keratinization is pronounced, as a result of which the vascular network is not visible [36].

Manganotti’s abrasive pre-cancerous cheilitis. The foci are rounded or irregular in size, ranging in size from 0.5 to 1.5 cm with a polished pinkish-red bottom, slightly bleeding, especially after removing the crusts. The epithelium along the edges of erosion is hyperplastic [36].

Leukoplakia. Flat leukoplakia: white with a flat surface and moderate keratinization of the plaque, vascular pattern - specks and stripes. Verrucous leukoplakia: an unevenly towering silvery-white small-knobby focus with significant keratinization, the vascular network is not translucent. Erosive-ulcerative leukoplakia: the surface of leukokeratosis with ulceration, small-knobby relief with varying degrees of keratinization and various vascular architectonics. The causes of leukoplakia of the oral cavity can be chronic traumatization of OM by sharp edges of decayed teeth, improperly made prostheses, galvanic current that occurs in the presence of prostheses made of dissimilar metals. Leukoplakia (ICD: K13.2) is a clinical term to describe white patches or plaques on the mucosal surface. In relation to the oral mucosa, the term "leukoplakia" is used in a narrow sense and includes only white spots or plaques that do not scrape off and do not refer to other diseases. Women with leukoplakia have a higher risk of developing carcinoma [36].

Leukoplakia resembles lichen planus, candidiasis, white spongy nevus. This term, regardless of the presence of epithelial dysplasia, is used solely for clinical description, and not to designate early anaplastic changes. The transformation of leukoplakia into cancer depends on its form and duration of the course.

5. Conclusions

Detection of human papillomavirus in patients with precancers of the oral cavity was 73.3% (22 cases). The fact of the presence of the virus can be used as an unfavorable prognostic sign of the course of the disease, the development of adequate terms for attendance at control dispensary examinations. The study showed that human papillomavirus can be correlated with a favorable prognosis of the disease. In case of virus-associated tumors of the oral mucosa, it is necessary to include in the treatment plan, with prior consultation with a virologist, an antiviral therapy regimen.

Such a late diagnosis, as a rule, presupposes treatment in the form of very traumatic surgical interventions, the results of which, nevertheless, remain unsatisfactory - the incidence and mortality from malignant neoplasms of OM are characterized by a steady upward trend. At the same time, the issues of epidemiology are no less important, since without a clear idea of the prevalence of the process, the stages, the histological affiliation of a particular tumor, it is impossible to solve problems such as prevention and early detection of malignant neoplasms. That is, an effective tumor prevention system is unthinkable without a well-established oncological statistics service, which is one of the mandatory components in the complex of anti-cancer measures. Considering that the oral mucosa is most susceptible to the action of exogenous carcinogens, it should be noted that the special role of the environmental situation in the development of malignant neoplasms.