cancer

Mesothelioma

2008-09-19T01:47:00.004-07:00

Mesothelioma is a form of cancer that is almost always caused by previous exposure to asbestos. In this disease, malignant cells develop in the mesothelium, a protective lining that covers most of the body's internal organs. Its most common site is the pleura (outer lining of the lungs and internal chest wall), but it may also occur in the peritoneum (the lining of the abdominal cavity), the pericardium (a sac that surrounds the heart) or tunica vaginalis.

Most people who develop mesothelioma have worked on jobs where they inhaled asbestos particles, or they have been exposed to asbestos dust and fibre in other ways, such as by washing the clothes of a family member who worked with asbestos. Unlike lung cancer, there is no association between mesothelioma and smoking.[1] Compensation via asbestos funds or lawsuits is an important issue in mesothelioma (see asbestos and the law).

The symptoms of mesothelioma include shortness of breath due to pleural effusion (fluid between the lung and the chest wall) or chest wall pain, and general symptoms such as weight loss. The diagnosis may be suspected with chest X-ray and CT scan, and is confirmed with a biopsy (tissue sample) and microscopic examination. A thoracoscopy (inserting a tube with a camera into the chest) can be used to take biopsies. It allows the introduction of substances such as talc to obliterate the pleural space (called pleurodesis), which prevents more fluid from accumulating and pressing on the lung. Despite treatment with chemotherapy, radiation therapy or sometimes surgery, the disease carries a poor prognosis. Research about screening tests for the early detection of mesothelioma is ongoing.
Contents
[hide]

Classification

2008-09-19T01:47:00.003-07:00

Cancer is generally classified according to the tissue from which the cancerous cells originate, the primary tumor, as well as the normal cell type they most resemble. These are location and histology, respectively.

Nomenclature

The following closely related terms may be used to designate abnormal growths:

* Tumor: originally, it meant any abnormal swelling, lump or mass. In current English, however, the word tumor has become synonymous with neoplasm, specifically solid neoplasm. Note that some neoplasms, such as leukemia, do not form tumors.
* Neoplasm: the scientific term to describe an abnormal proliferation of genetically altered cells. Neoplasms can be benign or malignant:
o Malignant neoplasm or malignant tumor: synonymous with cancer.
o Benign neoplasm or benign tumor: a tumor (solid neoplasm) that stops growing by itself, does not invade other tissues and does not form metastases.
* Invasive tumor is another synonym of cancer. The name refers to invasion of surrounding tissues.
* Pre-malignancy, pre-cancer or non-invasive tumor: A neoplasm that is not invasive but has the potential to progress to cancer (become invasive) if left untreated. These lesions are, in order of increasing potential for cancer, atypia, dysplasia and carcinoma in situ.

The following terms can be used to describe a cancer:

* Screening: a test done on healthy people to detect tumors before they become apparent. A mammogram is a screening test.
* Diagnosis: the confirmation of the cancerous nature of a lump. This usually requires a biopsy or removal of the tumor by surgery, followed by examination by a pathologist.
* Surgical excision: the removal of a tumor by a surgeon.
o Surgical margins: the evaluation by a pathologist of the edges of the tissue removed by the surgeon to determine if the tumor was removed completely ("negative margins") or if tumor was left behind ("positive margins").
* Grade: a number (usually on a scale of 3) established by a pathologist to describe the degree of resemblance of the tumor to the surrounding benign tissue.
* Stage: a number (usually on a scale of 4) established by the oncologist to describe the degree of invasion of the body by the tumor.
* Recurrence: new tumors that appear at the site of the original tumor after surgery.
* Metastasis: new tumors that appear far from the original tumor.
* Transformation: the concept that a low-grade tumor transforms to a high-grade tumor over time. Example: Richter's transformation.
* Chemotherapy: treatment with drugs.
* Radiation therapy: treatment with radiations.
* Adjuvant therapy: treatment, either chemotherapy or radiation therapy, given after surgery to kill the remaining cancer cells.
* Prognosis: the probability of cure after the therapy. It is usually expressed as a probability of survival five years after diagnosis. Alternatively, it can be expressed as the number of years when 50% of the patients are still alive. Both numbers are derived from statistics accumulated with hundreds of similar patients to give a Kaplan-Meier curve.

Cancers are classified by the type of cell that resembles the tumor and, therefore, the tissue presumed to be the origin of the tumor. Examples of general categories include:

* Carcinoma: Malignant tumors derived from epithelial cells. This group represents the most common cancers, including the common forms of breast, prostate, lung and colon cancer.
* Sarcoma: Malignant tumors derived from connective tissue, or mesenchymal cells.
* Lymphoma and leukemia: Malignancies derived from hematopoietic (blood-forming) cells
* Germ cell tumor: Tumors derived from totipotent cells. In adults most often found in the testicle and ovary; in fetuses, babies, and young children most often found on the body midline, particularly at the tip of the tailbone; in horses most often found at the poll (base of the skull).
* Blastic tumor or blastoma: A tumor (usually malignant) which resembles an immature or embryonic tissue. Many of these tumors are most common in children.

Malignant tumors (cancers) are usually named using -carcinoma, -sarcoma or -blastoma as a suffix, with the Latin or Greek word for the organ of origin as the root. For instance, a cancer of the liver is called hepatocarcinoma; a cancer of the fat cells is called liposarcoma. For common cancers, the English organ name is used. For instance, the most common type of breast cancer is called ductal carcinoma of the breast or mammary ductal carcinoma. Here, the adjective ductal refers to the appearance of the cancer under the microscope, resembling normal breast ducts.

Benign tumors (which are not cancers) are named using -oma as a suffix with the organ name as the root. For instance, a benign tumor of the smooth muscle of the uterus is called leiomyoma (the common name of this frequent tumor is fibroid). Unfortunately, some cancers also use the -oma suffix, examples being melanoma and seminoma.

Adult cancers

cancer

2008-09-19T01:47:00.002-07:00

Cancer (medical term: malignant neoplasm) is a class of diseases in which a group of cells display uncontrolled growth (division beyond the normal limits), invasion (intrusion on and destruction of adjacent tissues), and sometimes metastasis (spread to other locations in the body via lymph or blood). These three malignant properties of cancers differentiate them from benign tumors, which are self-limited, do not invade or metastasize. Most cancers form a tumor but some, like leukemia, do not. The branch of medicine concerned with the study, diagnosis, treatment, and prevention of cancer is oncology.

Cancer may affect people at all ages, even fetuses, but the risk for most varieties increases with age.[1] Cancer causes about 13% of all deaths.[2] According to the American Cancer Society, 7.6 million people died from cancer in the world during 2007.[3] Cancers can affect all animals.

Nearly all cancers are caused by abnormalities in the genetic material of the transformed cells. These abnormalities may be due to the effects of carcinogens, such as tobacco smoke, radiation, chemicals, or infectious agents. Other cancer-promoting genetic abnormalities may be randomly acquired through errors in DNA replication, or are inherited, and thus present in all cells from birth. The heritability of cancers are usually affected by complex interactions between carcinogens and the host's genome. New aspects of the genetics of cancer pathogenesis, such as DNA methylation, and microRNAs are increasingly recognized as important.

Genetic abnormalities found in cancer typically affect two general classes of genes. Cancer-promoting oncogenes are typically activated in cancer cells, giving those cells new properties, such as hyperactive growth and division, protection against programmed cell death, loss of respect for normal tissue boundaries, and the ability to become established in diverse tissue environments. Tumor suppressor genes are then inactivated in cancer cells, resulting in the loss of normal functions in those cells, such as accurate DNA replication, control over the cell cycle, orientation and adhesion within tissues, and interaction with protective cells of the immune system.

Diagnosis usually requires the histologic examination of a tissue biopsy specimen by a pathologist, although the initial indication of malignancy can be symptoms or radiographic imaging abnormalities. Most cancers can be treated and some cured, depending on the specific type, location, and stage. Once diagnosed, cancer is usually treated with a combination of surgery, chemotherapy and radiotherapy. As research develops, treatments are becoming more specific for different varieties of cancer. There has been significant progress in the development of targeted therapy drugs that act specifically on detectable molecular abnormalities in certain tumors, and which minimize damage to normal cells. The prognosis of cancer patients is most influenced by the type of cancer, as well as the stage, or extent of the disease. In addition, histologic grading and the presence of specific molecular markers can also be useful in establishing prognosis, as well as in determining individual treatments.

2008-09-19T01:47:00.001-07:00

Genome study finds 100 new cancer genes

2008-09-19T01:47:00.000-07:00

Scientists have found more than 100 new genes that can cause cancer if they become mutated. The discovery was part of the largest survey of the human genome to date, which also suggests that the number of cancer genes is far larger than previously thought.

All cancers are thought to be caused by DNA mutations in specific genes. "Thus far, there are approximately 350 genes in the human genome that have been shown to be cancer genes," said Mike Stratton, co-leader of the Cancer Genome Project at the Wellcome Trust Sanger Institute, Cambridge. "This is from a full spec of around 25,000 genes in the human genome."

The cancer genes have been painstakingly identified during more than 25 years of research. But new technology is speeding up the process, allowing scientists to systematically identify all the genes in a cancer cell. These gene sequences can then be compared to healthy cells to identify differences in DNA.

Prof Stratton's team looked at a family of 500 genes that include protein kinases, molecules that act like switches. "This set of genes is known to regulate key functions in virtually all cell processes, growth, differentiation, telling cells to live and die," said Andrew Futreal of the Sanger Institute.

Mutations in some of these genes are already implicated in cancer. An example is the Braf gene - a mutation here is found in more than 60% of cases of the skin cancer malignant melanoma.

In the new study, researchers looked at more than 500 genes in about 200 samples of different types of cancer. The results, published today in Nature, showed about 1,000 mutations in the protein kinase genes of cancer cells. "We find evidence for approximately 100 new cancer genes - this is a larger number than we really expected to find," said Prof Stratton.

Based on previous research, Dr Futreal said he had only expected to find about 10 new cancer genes in their sample. The 1,000 mutations were classified in two categories: drivers and passengers. Driver mutations are the ones that cause cancer cells to grow whereas passengers make no contribution to cancers.

"It turns out that most mutations in cancers are passengers. However, buried among them are much larger numbers of driver mutations than anticipated. This suggests that many more genes contribute to cancer development than was thought," said Dr Futreal. The challenge in the future will be differentiating between driver and passenger mutations.

Another surprise was the way in which the mutations were spread among the cancers - in some samples, scientists found large numbers of mutations in a pattern they had never seen before. "The number and patterns of these mutations are an archaeological signature of something that has happened to that cancer in the past, something that has been implicated in its causation," said Prof Stratton.

Some of these causes, such as the drug a cancer has been treated with, ultraviolet light and cigarette smoke, can already be interpreted. But Prof Stratton said the new mutations would need further research to explain. "This must be telling us something about previous exposures, perhaps to environmental chemicals and also abnormalities of DNA repair in these cancers."