Defending Against Cancer's Spread
Researchers have gained valuable knowledge that allows them to prepare for-and possibly prevent-metastasis.
by Jon Nalick
In any battle, surprise-or the failure to achieve it-can mean the difference between victory and defeat.
The fight against cancer is no exception. Physicians often find themselves on the defense because they cannot precisely predict where a patient's cancer may spread-or even if it will spread.
But like generals facing an enemy that has used the same tactics too often, physicians and scientists have gained valuable experience that now allows them to prepare for, and in some cases prevent, a cancer's spread.
Derek Raghavan, M.D., Ph.D., professor of medicine and urology and chief of the division of medical oncology, says that physicians have learned that cancers often have an affinity for spreading to specific regions of the body.
"No one knows why, but it is the subject of a lot of research and we know well that tumors have a pretty set way of doing things," he says.
Cancers spread in a process called "metastasis" through one or more of three pathways. They can spread locally through tissues they touch directly, or they can travel to distant parts of the body through the lymphatic or circulatory systems.
Many kinds of cancer tend to spread in a particular way, often to the same specific sites. For example, prostate cancer often spreads to lymph nodes and bone. On the other hand, breast cancer preferentially spreads to the liver and lungs.
Knowing how and where a patient's tumor is likely to spread can help physicians tailor treatment to make it more effective, less invasive and less costly.
"In prostate cancer, you're more likely to use a bone scan because that's a likely site for it to spread. But in testicular cancer, you would never order a bone scan because that's an extremely uncommon place for it to go," Raghavan says.
Also, knowing that a cancer has metastasized often suggests a different course of treatment.
"For example, a breast cancer that is localized can be cured by lumpectomy and radiation alone. But a breast cancer that has metastasized may also be treated with a combination of hormones and chemotherapy," he says.
Cancers that commonly spread to specific sites include:
o Lung cancer: to the liver, bones, brain and adrenal glands;
o Breast cancer: bones, liver, and sometimes the brain;
o Prostate cancer: lymph nodes and bones.
Unfortunately, some of the deadliest cancers, including melanomas and lymphomas, can spread anywhere in the body, Raghavan says.
Raghavan says that although no one knows why certain cancers preferentially spread to specific sites, one hypothesis suggests that they take root in environments most similar to their origin.
Lung cancers, for example, may have an affinity for the brain because both the lung and brain are well-oxygenated environments with an abundance of blood vessels.
However, some cancers, such as prostate cancer that often spreads to the bone, violate that pattern, so USC researchers continue to examine the factors involved in metastasis.
Peter Brooks, Ph.D., assistant professor of biochemistry, and Parkash Gill, associate professor of medicine and pathology, are focusing on how blood vessels grow and how they can contribute to a tumor's spread.
Angiogenesis-the recruitment of new blood vessels-is important because tumors rely on the process for nourishment and use the blood vessels to metastasize. Blocking the growth can potentially starve and shrink the tumor and perhaps even stop metastasis. That, in turn, might make the tumor vulnerable to conventional cancer therapies.
For all of these scientists, knowledge is the best defense in their battle to fight cancer.