What is metastasis?

What is cancer?

The word cancer is derived from the Latin word for crab because cancers are often very irregularly shaped, and because, like a crab, they "grab on and don't let go." The term cancer specifically refers to a new growth which has the ability to invade surrounding tissues, metastasize (spread to other organs) and which may eventually lead to the patient's death if untreated.

The terms tumor and cancer are sometimes used interchangeably which can be misleading. A tumor is not necessarily a cancer. The word tumor simply refers to a mass. For example, a collection of fluid would meet the definition of a tumor. A cancer is a particularly threatening type of tumor. It is helpful to keep these distinctions clear when discussing a possible cancer diagnosis.

What is metastasis?

When cancer spreads from the part of the body where it started (its primarysite) to other parts of the body it is calledmetastasis. Metastasis can occur when cells break away from a cancerous tumor and travel through the bloodstream or through lymph vessels to other areas of the body. (Lymph vessels are much like blood vessels, except they carry a clear fluid called lymph back toward the heart.) Cancer cells that travel through the blood or lymph vessels can spread to other organs or tissues in distant parts of the body.

Many of the cancer cells that break off from the original tumor die without causing any problems. But some settle in a new area. There, they begin to grow and form new tumors. When cancer spreads, we say that it metastasizes. If there is only a single tumor, it?s called a metastasis or a metastatic tumor. When there are 2 or more metastatic tumors, it?s called metastases.

Sometimes metastatic tumors are found by tests done when the primary cancer is first diagnosed. In other cases, the metastasis is found first, causing the doctor to look for the place that the cancer started.

Sometimes, no metastases are seen when the cancer is first found. Instead, they are found later, after the patient has been treated and was thought to be cancer free. When a cancer has come back after treatment, it?s calledrecurrence. Recurrence is not the same as metastases ? it can also occur at or near the place the cancer started. When it does come back as metastases, it?s called a distant recurrence. For a cancer to recur as metastatic disease, some cancer cells had to have broken off from the primary tumor and survived the initial treatment. These cells traveled through the body and started growing in new places.

Different cancers tend to spread to different sites, but some of the most common sites of distant recurrence include the bones, liver, brain, and lungs.

Causes

A neoplasm can be caused by an abnormal proliferation of tissues, which can be caused by genetic mutations. Not all types of neoplasms cause a tumorous overgrowth of tissue, however (such as leukemia or carcinoma in situ).

Recently, tumor growth has been studied using mathematics and continuum mechanics. Vascular tumors (formed from blood vessels) are thus looked at as being amalgams of a solid skeleton formed by sticky cells and an organic liquid filling the spaces in which cells can grow.^[13] Under this type of model, mechanical stresses and strains can be dealt with and their influence on the growth of the tumor and the surrounding tissue and vasculature elucidated. Recent findings from experiments that use this model show that active growth of the tumor is restricted to the outer edges of the tumor, and that stiffening of the underlying normal tissue inhibits tumor growth as well.^[14]

Benign conditions that are not associated with an abnormal proliferation of tissue (such as sebaceous cysts) can also present as tumors, however, but have no malignant potential. Breast cysts (as occur commonly during pregnancy and at other times) are another example, as are other encapsulated glandular swellings (thyroid, adrenal gland, pancreas).

Encapsulated hematomas, encapsulated necrotic tissue (from an insect bite, foreign body, or other noxious mechanism), keloids (discrete overgrowths of scar tissue) and granulomas may also present as tumors.

Discrete localized enlargements of normal structures (ureters, blood vessels, intrahepatic or extrahepatic biliary ducts, pulmonary inclusions, or gastrointestinal duplications) due to outflow obstructions or narrowings, or abnormal connections, may also present as a tumor. Examples are arteriovenous fistulae or aneurysms (with or without thrombosis), biliary fistulae or aneurysms, sclerosing cholangitis, cysticercosis or hydatid cysts, intestinal duplications, and pulmonary inclusions as seen with cystic fibrosis. It can be dangerous to biopsy a number of types of tumor in which the leakage of their contents would potentially be catastrophic. When such types of tumors are encountered, diagnostic modalities such as ultrasound, CT scans, MRI, angiograms, and nuclear medicine scans are employed prior to (or during) biopsy and/or surgical exploration/excision in an attempt to avoid such severe complications.

The nature of a tumor is determined by imaging, by surgical exploration, and/or by a pathologist after examination of the tissue from a biopsy or a surgical specimen.

Date: 2016-06-13; view: 148