Structural Biochemistry/Carcinoma

Definition

Carcinoma, the most common type of cancer that occurs in humans, is the classification of cancer that is derived from epithelial cells. It refers to the tumor tissue that is composed of epithelial cells that have altered or damaged genomes that lead the cell to exhibit detrimental and malignant properties.

Adrenocortical carcinoma, which arises from the adrenal cortex, the outside layer of the adrenal gland. The cells in the adrenal cortex make hormones that help the body work properly, such as steroids and hormones important for sexual development and maturation. When cells in the adrenal cortex become cancerous, they may make too much of one or more hormones, which can cause symptoms such as high blood pressure, weakening of the bones, or diabetes. If male or female hormones are affected, the body may go through changes such as a deepening of the voice, growing hair on the face, swelling of the sex organs, or swelling of the breasts. Thyroid carcinoma: arises from the thyroid, a gland located in the neck that manufactures hormones that affect heart rate, body temperature, energy level, and also control the level of calcium in the blood. Nasopharyngeal carcinoma: affects the nose and pharynx. Malignant melanoma: a cancer of the skin.

Incidence: Contrary to what occurs in adults, where carcinomas are the most common cancers, among children, particularly before the adolescent years, carcinomas are extremely rare. In the United States, about 1,050 children and adolescents are diagnosed with carcinomas each year. Of these, about 350 (35.5 percent) are thyroid carcinomas and 300-350 (30.9 percent) are melanomas. Adrenocortical carcinomas (1.3 percent), nasopharyngeal carcinomas (4.5 percent), other skin carcinomas (0.5 percent), along with other and unspecified (27.3 percent) make up the rest. All of the carcinomas represent only 9 percent of all cancers in children. Nearly 75 percent (2,047) of the childhood carcinomas occur in adolescents (15-19 years old), including 75 percent of the thyroid carcinomas, 80 percent of the melanomas, 63 percent of the nasopharyngeal carcinomas, and 74 percent of the other and unspecified carcinomas.

Influencing Factors: The most well established risk factor for thyroid carcinoma is exposure to ionizing radiation, from both environmental and therapeutic sources. The primary risk factor for melanoma is sun exposure. Nasopharyngeal carcinoma appears to be associated with infection by the Epstein-Barr virus.

Survival Rates: Outcome for patients with adrenocortical carcinoma that can be completely resected is usually very good. However, when the tumor cannot be completely removed, or when it comes back after surgery, the prognosis is much worse. For patients with nasopharyngeal carcinoma, treatment with chemotherapy and radiation therapy usually provides survival rates of 70 to 75 percent. The outcome for patients with thyroid cancer is also excellent with appropriate therapy.

Treatment Strategies: For adrenocortical carcinoma, surgery is the primary treatment. When tumors cannot be removed or have already spread to other sites, chemotherapy is recommended. However, adrenocortical carcinoma is not very sensitive to chemotherapy, therefore the prognosis for these patients is poor. For patients with nasopharyngeal carcinoma, surgery is not possible due to the location of the tumor and the fact that it infiltrates the tissues and lymph nodes of the neck. These patients are treated with chemotherapy and radiation therapy to the nasal and pharyngeal cavities as well as the entire neck. Thyroid carcinoma can usually be treated with surgery alone. When thyroid cancer has spread to the lymph nodes of the neck or to the lungs, treatment can be given with iodine molecules that have a radioactive component.

Current Research: For adrenocortical carcinoma, St. Jude is currently leading a study in collaboration with American and Brazilian institutions, in which a comprehensive approach to the treatment of this cancer is proposed, including new surgery techniques and uniform chemotherapy regimens. Researchers at St. Jude are growing tumor cells in cultures to study new drugs for treatment. St. Jude participated in the discovery of a new gene mutation in some patients. This unique mutation provides new insights into the mechanism for cancer development. An epidemiological genetic study is being held to understand more about this gene mutation and its role to the incidence, early diagnosis and treatment of disease. Epidemiology is a branch of medical science that deals with the incidence, distribution, and control of disease in a population.

Origin

Carcinoma can be defined as a cancer that expresses characteristics that include malignant tumors, but it is still classified as a "cancer of unknown primary origin," also known as CUP. Despite the fact that the origin and developmental lineage is still unknown, the cells affected by carcinoma still exhibit specific cellular, histological, and molecular characteristics that are deemed as normal within epithelial cells. These characteristics include keratin pearls, intermediate filaments, tissue architectural motifs, and intercellular bridge structures.

Diagnosis

Typically, carcinomas can be diagnosed through the process of biopsy, which may include subtotal removal of a single node, core biopsy, and fine-needle aspiration. After the biopsy, a pathologist usually plays the role in identifying the cellular, molecular, and tissue properties of the epithelial cells that are to be examined.

Common Sites of Carcinoma

• Breast: Almost all breast cancers fall under the category of ductal carcinoma.
• Colon: Almost all colon cancers are due to adenocarcinoma or squamous cell carcinoma.
• Lungs: Most types of lung cancers are exhibited through small-cell lung carcinoma.
• Pancreas: Nearly all pancreatic cancers fall under adenocarcinoma and are lethal.
• Prostate: Many forms of prostate cancer would fall under the category of adenocarcinoma.
• Rectum: Almost all rectum cancers are due to adenocarcinoma or squamous cell carcinoma.

Carcinoma in situ

Carcinoma in situ (CIS) is defined by a regional, miniature carcinoma that has not gone through the stages of invading the membrane of an epithelial cell. It is usually described as a pre-invasive cancer and not necessarily detrimental to the whole system of cells. If left untreated, the CIS will almost always continue to go through the regular process of penetration into the membrane and other structures, thus making it a truly invasive carcinoma. The lesion of the carcinoma can typically be removed through surgery, before the invasion process occurs. On some occasions, the CIS lesion may exhibit less aggressiveness and return to the more normal molecular characteristics.

References

1. http://www.medterms.com/script/main/art.asp?articlekey=20677
2. Berman JJ (March 2004). "Tumor classification: molecular analysis meets Aristotle". BMC Cancer 4: 10. doi:10.1186/1471-2407-4-10. PMC 415552. PMID 15113444.