Genetic Considerations of Diseases and Disorders that Affect the Oral Cavity
Part II. Oral Cancer and Developmental Disorders
CANCER
OF THE ORAL CAVITY
Cancers involve body tissues whose
cells are dividing and growing faster
than cells are dying. The result
of excessive cell growth is an enlarged
mass called a tumor. Cancers may
fail to remain within the boundaries
of normal tissues and therefore
spread or invade surrounding healthy
tissues. Unfortunately, cancer of
the head and neck is diagnosed relatively
frequently. The most common oral
cancers involve the surface tissue
(epithelium) of the mouth and pharynx.
RISKS FACTORS
FOR DEVELOPING ORAL CANCER
Genetic Factors. Genetic factors involved in the development of cancer include:
Tobacco
and Alcohol. Use of tobacco
and alcohol are the major risk factors
for developing oral cancer. Tobacco
and alcohol contains substances
that are carcinogenic or promote
cancer. Cigarettes smoke and substances
in smokeless tobacco have received
considerable attention as carcinogens
that promote oral cancer. Studies
also indicate that smoking in combination
with consumption of alcohol produces
an even greater risk for oral cancer
than use of either substance alone.
Radiation. Radiation of high dosage and prolonged duration can produce cancer. There is no evidence that routine dental X-rays are carcinogenic, especially with today's high speed, low dosage machines.
Traumatic irritation. Prolonged irritation from broken teeth, rough dental restorations, and ill-fitting dentures are considered a possible causes for oral cancer.
Viruses. Some viruses can cause cancer in human cells. Studies have indicated a link to oral cancer with infections from herpes simplex type- I virus, Epstein-Barr virus, and human papillomavirus.
DIAGNOSIS AND
EVALUATION
Early diagnosis
is the single factor in successfully
combating oral cancer. Therefore,
it is crucial that the patient seeks
immediate and proper treatment for
the disease. If tissue of the mouth
is suspected to be cancerous, a
biopsy is necessary. A biopsy involves
surgically removing diseased tissue
for microscopic evaluation and diagnosis
by a pathologist.
PRE-CANCEROUS
LESIONS OF THE MOUTH
Pre-cancerous
refers to early changes of normal
cells that are changing into cancer
cells. Recognition of pre-cancerous
tissue of the mouth is an important
role in the diagnosis and prevention
of oral cancer by the dental health
professional. Many times, pre-cancerous
tissue goes unnoticed by an individual
because it is not painful. As a
general rule, pre-cancerous or early
cancers do not heal.
Leukoplakia. Leukoplakia is a term that describes a 'white patch' on the surface of oral tissues. Leukoplakias have been associated with pre-cancerous tissues. In general, leukoplakias are suspected as pre- or early cancer if the white area cannot be scraped off the surface tissue and cannot be attributed to another disease.
Erythroplakia. Erythroplakia occurs in the oral cavity as a distinct and well-defined patch with a bright red and velvety surface. Erythroplakias are relatively rare lesions of the oral cavity. Erythroplakias are almost always pre-cancerous.
DESCRIPTION
OF SELECTED ORAL CANCERS
Cancers can involve
growth changes to any tissue of
the oral cavity. Cancers of the
mouth may be benign or malignant
tumors. A benign tumor is a mass
limited within a connective tissue
capsule. This type of tumor does
not spread or invade adjacent tissue
and is therefore usually not life-threatening.
A malignant tumor, on the other
hand, is a mass capable of spreading
and invading other healthy tissues
of the body. The spread of cancer
cells occurs by traveling within
the bloodstream or lymph system.
A malignant tumor can then form
additional sites of cancers away
from the original tumor, a
process called metastasis. Malignant
tumors are dangerous and difficult
to control. Well-developed malignant
cancers can be life threatening.
Squamous
Cell Carcinoma. Squamous
cell carcinoma is the most frequently
occurring malignant cancer of the
oral region. This type of cancer
involves cell growth changes of
the surface tissue of the oral region,
the epithelium. Nearly 90% of all
oral cancers are squamous cell carcinomas.
The most frequent location of this
cancer is on the lips, the tongue,
and the floor of the mouth. A chronic
(long-term) mouth ulcer that does
not heal, a lesion attached to deeper
tissues, and a red-velvety lesion
are all suspect squamous cell carcinomas.
If left untreated, squamous cell
carcinomas undergo metastasis and
involve vital organs of the body.
Many times death is the result of
complications to the heart and lungs.
Basal Cell
Carcinoma. Basal cell carcinoma
is a tumor located on the surface
of skin that has hair. Basal cell
carcinomas are associated with prolonged
exposure of skin to the sun. Lesions
initially appear as elevated blisters,
followed by a period of ulceration
and healing. Continued cycles of
blistering, ulcerating, and healing
of the same tissue occurs as deeper
tissues are slowly invaded. Metastasis
of basal cell carcinomas is rare, and survival rate of individuals diagnosed
with basal cell carcinoma is excellent.
Fibromas.
Fibromas are benign tumors
whose cell origin lies in the connective
tissue supporting teeth within tooth
sockets, the periodontal membrane.
Osteomas.
Osteomas are benign tumors
whose cell origin is the bone of
the upper and lower jaw.
Malignant
tumors of connective tissue origin.
Malignant tumors of connective tissue
origin (the periodontal membrane,
bone and cartilage) include fibrosarcomas,
osteosarcomas and chondrosarcomas.
Tumors of
the teeth. Tumors involving
cells of the teeth are termed odontogenic
tumors.
Salivary gland
tumors. Salivary gland tumors
are varied in their degree of malignancy
and tumor cell origin. Salivary
gland tumors can be benign or malignant.
This type of tumor is very rare.
TREATMENT OF
ORAL CANCER
The three major
treatment considerations for oral
cancer include:
- Surgical removal of diseased tissue. This is the best management for treatment of cancer if possible. The advantages for surgery are prompt treatment and the ability of physicians to study tissue removed during surgery with a microscope. With this study, it can be known that the entire tumor has been removed. The disadvantage of surgical treatment is normal tissue loss in the attempt to remove all diseased tissue. Another consequence to surgery is the risk of loss of function and cosmetic defects.
- Radiation therapy. This is an effective form of treatment for isolated areas of cancer. As the size of the tumors enlarge, larger doses of radiation are necessary to kill cancer cells. The advantages of radiation therapy are the preservation of normal tissues and the maintenance of normal tissue function. The major disadvantage of radiation therapy includes inflammation of the lining of the mouth, destruction of salivary gland tissue that can result in dry mouth, changes in taste sensations, dental decay, damage to small blood vessels, and the risk of necrosis to bone tissue.
- Chemotherapy. Chemotherapy is dependent on the cancer diagnosis. Therapy can be designed for a systemic approach (one that treats the entire body) or a regional approach (one that treats the only the area of the cancer). The appropriate medication and duration of treatment is determined by evaluating the location of the cancer and the severity of the disease process. There are many side effects to chemotherapy, including complications affecting cells of the bone marrow, the gut, and lining of the mouth.
Treatment of most cancers of the head and neck involve a combination of surgery, radiation and chemotherapy.
DEVELOPMENTAL
DISORDERS OF THE HEAD
Developmental
disorders of the head (craniofacial
region) are the result of problems
that occur during development and
growth of a baby prior to birth.
Genes responsible for formation
of the head very early in pregnancy
(approximately three weeks following
conception) are also responsible
for the development of limbs and
vital organs, such as the heart
and lungs. Therefore, craniofacial
defects are many times components
of other developmental defects.
Many studies conclude that developmental
defects result from the interaction
of multiple genes and environmental
factors.
DESCRIPTION
OF SELECTED DEVELOPMENTAL DEFECTS
Cleft Lip
and Cleft Palate.
The most common of all craniofacial
defects is the cleft lip and cleft
palate. Clefting, or incomplete
fusion of the lip and/or palate,
can occur alone or as part of a
hereditary syndrome. The pattern
of inheritance in cleft lip and
cleft palate suggests that up to
twenty genes are involved with this
defect.
Craniosynostoses. Craniosynostoses is a genetic disorder that causes early fusion of the bones surrounding and protecting the brain (bones of the skull). As a result, dangerous amounts of pressure are created against an enlarging brain within a braincase that is not growing. Several hereditary syndromes include mental retardation due to craniosynostoses as a characteristic feature.
Hereditary Anodontia. Conditions of the complete absence of teeth (anodontia) have been correlated to specific genes. The complete absence of teeth alters bone development within the upper and lower jaws of the mouth.
Amelogenesis Imperfecta and Dentinogenesis Imperfecta. Amelogenesis imperfecta is a genetic disorder that results in defective enamel formation of teeth. Enamel is the hard surface covering the crowns of teeth. Amelogenesis imperfecta either causes problems in enamel hardening (mineralization) of normal amounts of enamel or causes a smaller amount of normal enamel to be produced. Dentinogenesis imperfecta is a genetic disorder that results in defective dentin formation within teeth. Dentin is a mineralized material forming the bulk of each tooth. Defective dentin causes the normal enamel layer that covers the tooth to flake off. In both diseases, the teeth are weak and very sensitive to temperature and pressures. Amelogenesis imperfecta and dentinogenesis imperfecta are linked to defects in structural genes that code for proteins necessary for the development of enamel and dentin.
Osteogenesis Imperfecta. Osteogenesis imperfecta is an inherited disease caused by mutations of genes that produce collagen. Collagen is an important substance within connective tissues of the body such as bone. Osteogenesis imperfecta causes 'brittle bone' diseases that affect all bones of the body. A complication of osteogenesis imperfecta that involves tissues of the mouth in addition to the more generalized effect of fragile bones is a painful dentinogenesis imperfecta-like change in the teeth.
REFERENCES
Blot, W.J., J.K.
McLaughlin, D.M. Winn, D.F. Austin,
R.S. Greenberg, S. Preston-Martin,
L. Bernstein, J.B. Schoenberg, A.
Stemhagen, and J.F. Fraumeni. 1988.
Smoking and drinking in relation
to oral and pharyngeal cancer. Cancer
Research 48:3282-3287.
Bricker, S.L., R.P. Langlais and C.S. Miller. 1994. Oral Diagnosis, Oral Medicine, and Treatment Planning, Second Edition. Philadelphia, Lea and Febiger Publishing.
Greenblatt, M.S., W.P. Bennett, M. Hollstein, C.C. Harris. 1994. Mutations in the p53 tumor suppressor gene: clues to cancer etiology and molecular pathogenesis. Cancer Research 54(18):4855-4878.
Lidral, A.C., J.C. Murray, K.H. Buetow, A.M. Basart, H. Schearer, R. Schiang, A. Naval, E. Layda, K. Magee, W. Magee. 1997. Studies of the candidate genes TGFB2, MSX1, TGFA, and TGFB3 in the etiology of cleft lip and palate in the Philippines. Cleft Palate - Craniofacial Journal 34(1):1-6.
Shklar G. 1986. Oral Leukoplakia. New England Journal of Medicine 315(24):1544-1546.
Spandidos D.A. A. Lamothe, J.K. Field. 1985. Multiple transcriptional activation of cellular oncogenes in human head and neck solid tumors. Anticancer Research 5(2):221-224.
U.S. Department of Health and Human Services. 2000. Oral Health in America: A Report of the Surgeon General. U.S. Public Health Service.
HOW TO LEARN
MORE
www.ADA.org
This is the American Dental Association
website, which provides access to
news and publications related to
dental health
www.aaoms.org This is the American Association of Oral and Maxillofacial Surgeon website, which contains information about oral and maxillofacial surgery including oral cancer.
www.tonguecancer.com This site provides diagnosis and treatment for cancers of the head and neck.
www.clapa.cwc.net This is the Cleft Lip and Palate Association website, which provides information and support to anyone with or affected by cleft lip and clept palate
www.cleftline.org This is the American Cleft Palate-Craniofacial Association website. This national organization provides lay and professional services for cleft lip, cleft palate, and other craniofacial defects.
ABOUT THE AUTHOR
S. Michele Robichaux,
D.D.S, is an associate professor
of biology at Nicholls State University
in Thibodaux, Louisiana. She teaches
Human Anatomy, Physiology and Histology.
Her research interests include the
genetics and microbiology of periodontal
disease.
CONTACT THE
AUTHOR
Dr. S. Michele
Robichaux
Department of Biological Sciences
Nicholls State University
Thibodaux, LA 70310
(985) 448-4721
biol-smr@nicholls.edu
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