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Medical Video: Introduction to Cancer Biology (Part 3): Tissue Invasion and Metastasis
The main reason why cancer is so feared is because it can spread widely in the body. Cancer usually starts with one tumor in a specific area of the body, such as the breast. If the tumor is not removed, the cancer can spread to nearby organs and other places far from the initial tumor location.
How can cancer spread to new areas and why are some organs more likely to be infected than others? Here's the explanation.
How can cancer spread?
The spread of cancer throughout the body is known as metastasis. The spread of cancer begins when cancer cells separate from the initial tumor, and invade nearby normal tissue. From here, cancer cells then multiply and may produce certain compounds that stimulate cell movement to other places. Cancer cells can spread through one of several common metastatic routes (blood flow, lymphatic system, or penetrate the covering layer of body organs) to go to other parts of the body.
This is a fairly complicated journey and most cancer cells cannot survive. Some cancer cells may be killed by the immune system or trapped in lymph nodes for destruction, but some can survive and grow to form new tumors. Of the thousands of cancer cells that successfully release from mother cancer, maybe there will only be a few that can survive to form secondary (metastatic) cancer.
Once in a new place, cancer cells begin to multiply to form small tumors called micrometastases. This small tumor group then joins and grows into "adult" tumor cells, and completes the metastatic cycle process. When observed under a microscope and tested in certain ways, metastatic cancer cells carry characteristics that resemble maternal cancer, rather than resembling the characteristics of cells in a new place where metastatic cancer is found. This is a sign that doctors can ensure that the cancer is a cancer that has spread from core sources elsewhere from the body, and is not a completely new type of cancer.
Metastasis is an important factor in the development of cancer because metastasis is responsible for the majority of cancer deaths. In most cases, cancer patients with local tumors have the opportunity to survive better than metastatic tumors.
What causes cancer to spread?
Stephen Paget, a British surgeon, theorizes that cancer cells find it difficult to survive in an external environment that is completely different from the characteristics of a parent tumor. Therefore, cancer can only spread to locations that have the same cell characteristics. For example, breast cancer cells need calcium ions from the breast mammary gland to multiply, so that breast cancer cells may prefer bone as the location of its spread because the bones are rich in calcium.
James Ewing, professor of first pathology at Cornell University, proposed another theory that cancer cells tend to attack regional lymph nodes near the primary tumor. So, patients with primary tumors that are passed by the vessels leading to the lungs will eventually develop lung metastatic cancer.
One study from University College London (UCL), reported from Medical Daily, said they have found a mechanism that causes the spread of cancer. Through testing laboratory animals, it was found that cancer cells began to spread when healthy cells began to disperse in an effort to avoid dangerous attacks. Cancer cells are attracted to healthy cells and continue to follow the movement of healthy cells throughout the body.
All the above theories contain truth. However, the big picture of the cancer metastasis process is far more complicated than imagined.
What cancer sufferers are more at risk of developing cancer that spreads?
Having active cancer or a history of having cancer is a major risk factor for experiencing the spread of cancer. Some types of cancer are more likely to spread than others. However, the level of ability of the spread of cancer cells will vary between one type of tumor and the other.
For example, basal cell carcinoma rarely spreads, but cancer of the pancreas, brain, and liver is a type of cancer that can spread rapidly. Different types of cancer have also been known to have "favorite" destinations for metastasis. For example, prostate cancer generally spreads to the bone, while intestinal cancer metastasizes to the liver.
Other factors, such as the nature of cancer cells, certain genetic changes, and the effectiveness of the body's immune system in removing cancer cells, also play a role in determining the success of metastasis. Where cancer cells spread will also depend on the type, size, and where the cancer cells begin in the body.
Even when these things are known, doctors are not always sure if someone's cancer will metastasize. Doctors aren't sure what causes some types of cancer to spread. And it's still unclear the reason behind why some cancers choose to walk spread to the bone rather than other public places to metastasize, such as the liver.
