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Oral Cancer Part I

Etiology

While oral cancer is a concern of global proportions, its incidence varies from country to country. According to recent reports, the incidence of oral and pharyngeal cancers--which had remained relatively static--is becoming more prevalent in women and younger patients. Oral cancer is the eighth most common form of cancer in the United States and Europe, and due to late detection, the survival rate is only 52%. New oral, laryngeal, and pharyngeal cancers are estimated to be diagnosed in 30,000 Americans and cause 8,000 deaths each year. Oral cancers often coexist as second primary cancers with other upper aerodigestive cancers (eg, larynx, esophagus, and lung), and are generally observed on the mouth, tongue, and lips.

Etiology

The objective of epidemiological analysis is to identify the relationship between the incidence of oral cancer and the particular risk factors. Immunocompromised patients, as well as those who use tobacco or heavily consume alcohol, are at particularly high risk for oral cancer. Diverse carcinogenic agents (eg, chemical products, radiation, ultraviolet light, and viruses) can also alter the biochemical structure of DNA and predispose a patient to cancer. Since the function of numerous chemical molecules in carcinogenesis is now well known, clinicians have an opportunity to institute preventive measures.

Genetic Factors

Cancers are the most frequent and complicated of the somatic genetic diseases,1 and are related to the acquisition of genetic anomalies by tumor cells. The hypothesis that the manifestation of cancer is related to a disturbance of the genome is reinforced when considering rare cancers, hereditary transmission, cancer augmentation, and the association between cancers and chromosomic modifications.2

Genetic analysis has recently expanded, and new techniques have improved genome exploration as DNA sequences and gene clones. Studies have demonstrated that transforming genes or oncogenes have sequences similar to "normal" genes, albeit with mutations. The introduction of these viral genes to the cells can provide the impetus necessary to create malignant cells. Cancer can be viewed as a disruption of the balance between oncogenes and antioncogenes. Research emphasizes the relationship between genetics and the progression of the cells toward malignancy. In clinical practice, the evaluation of genetic risk is essential and supports the necessity of early screening for at-risk patients. While only 5% to 10% of cancer is caused by hereditary factors that follow Mendel's law, the genetic structure influences the development of cancer.

Cancer Mechanism and Localization

Cancer occurs when cells become abnormal and divide without control. In a healthy person, cells divide and maintain the individual's cellular makeup. A tumor occurs as a result of uncontrolled mitosis that produces a mass of excessive tissue; this tissue must then be examined to determine if it is benign or malignant. Although the impetus that changes a normal cell into a tumor remains to be determined, the genes that initiate cancer have been identified. Clinical and experimental research indicate that the majority of all cancers are issued from a unique origin cell that proliferates as a clone, and each tumor exhibits characteristics of the origin cell. These cells also possess different properties, however, due to modifications caused by neoplastic cells that affect genotypic and phenotypic characteristics during the constitution of a cell. The genome of the cancer cell is completely unstable, and the cells exhibit chromosomal abnormality.

One important aspect of a tumor cell is its ability to proliferate outside the principles of homeostasis. In cancer cells, the disturbance of the regulatory process in the cellular cycle causes disorder in the synthesis of DNA, which allows the growth of the tumor and results in the instability of the genome. The cellular homogeneity of a cancer cell is accentuated and permits the selection of aggressive cells with new phenotypes that are able to resist chemotherapy and metastasize.

The initial morphological appearance of the tumor cell can be extremely similar to or different from that of a healthy cell. Neoplastic classifications of the cell are based on histogenesis, benign or malignant biological evaluation, anatomical location, and degree of differentiation. A tumor can originate in the epithelium, the mesenchyme, or from undetermined sources, and is classified according to its biological evolution. Benign tumors are limited in nature, grow slowly without aggression toward the host, are not recurrent following exeresis, and do not metastasize. Malignant tumors rapidly evolve and invade the tissues via infiltration and destruction. These tumors are also recurrent, can metastasize, and be fatal unless they receive treatment.

The preliminary diagnosis is essential to the prognosis of oral cancer. The anatomical site influences the tumor type, and the respective frequency of the different anatomopathological forms is characteristic of the organ or tissue type. Therefore, an upper aerodigestive site will manifest as epidermoid carcinoma. The clinical indication of the tumor proliferation depends on the clinical threshold form of each anatomical localization and consequently is variable. Tumor proliferation can be modified by numerous factors related either to the specific biology of the tumor cells or the host defense reactions.

Cancer cells synthesize enzymes that first destroy intercellular space and basal membranes and then proceed to destroy the adjacent tissues. During the progressive local extension of the invasive tumor, the dissemination of the tumor cells can occur when they quickly cross through low caliber, lymphatic, or venous vessels. The oral cavity is the seat of numerous inflammations, abnormal growth, ulcers, and infection. Most can be treated by medication and surgery, but undetected and untreated malignant tumors can invade and destroy adjacent structures and spread to nearby lymph nodes and distant sites. Secondary tumors are metastasized from the blood stream and the lymphatics. Morphologic and anatomical considerations are important in the establishment of the diagnosis, the histological prognosis, and the evolution to fatality. Many factors differentiate a benign tumor from a malignant tumor, but any one factor is specific enough to establish a diagnosis. The prognosis of a cancer tumor is based on histological factors (eg, size, proliferation, early metastases, treatment resistance). 

 * Continues to Part II - Identification and Treatment

 

References

  1. Janin N. Introduction au processus de la cancerogenese: Les cancers sont des maladies genetiques somatiques. Rev Med Interne 1994;15(12):821-829.
  2. Daly-Schveitzer N. Cancérologie Clinique: Abreges. Paris, France: Masson, 1994.
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