ASK THE EXPERTS

Q:How does chemotherapy work?

A:Chemotherapy is the treatment of cancer with drugs that can destroy cancer cells. Normal cells grow and die in a controlled way. When cancer occurs, abnormal cells continue to divide and proliferate without control. Chemotherapy destroys cancer cells by stopping them from growing or dividing. However, healthy cells may also be harmed, especially those that divide quickly. This is what causes side effects including fatigue, hair loss, nausea and vomiting. Normal cells usually repair themselves after chemotherapy.

Depending on the type of cancer and how advanced it is, chemotherapy may be used to achieve different goals. Treatment may be intended to cure the cancer. It may be intended to control the cancer by keeping the tumor from spreading or slowing its growth. It may also be used to relieve symptoms that the cancer may cause and help patients live more comfortably.

Chemotherapy is often used in combination with other therapies, including to shrink tumors before surgery or radiation (called neo-adjuvant therapy) or to destroy cancer cells that may remain after surgery or radiation (called adjuvant therapy). It also may be used to improve effectiveness of radiation therapy or to help destroy cancer if it recurs or spreads to other parts of the body away from the original tumor.

Research is leading to more targeted therapies that may attack cancer cells with few, if any, side effects to normal cells. Several studies are examining whether combining some of these new treatments with traditional chemo-therapy can fight cancer more effectively.

Dr. David H. Johnson
Cornelius Abernathy Craig Professor of Oncology
Deputy director, Vanderbilt-Ingram Cancer Center
Director, Division of Hematology-Oncology

Q:How is a star born, and what makes stars look like they're twinkling?

A: Stars are formed from the interstellar matter that is found in galaxies like our Milky Way. Most, if not all, new stars are products of the collapse of very large regions of galactic interstellar gas and dust called Giant Molecular Clouds (GMCs). When a GMC starts to collapse, due, say, to the energy acting on it from a nearby supernova explosion, it will fragment into many smaller, denser regions of gas and dust, each of which can continue to collapse and contract, gravitationally, until their internal temperatures and pressures are high enough to initiate the fusion of their hydrogen nuclei. Many astrophysicists will say that a star is "born" when this fusion begins in a collapsed fragment. This "birthing" process, from collapsing fragment to nuclear fusion, occurs quickly compared to the whole life history of a star. For example, our Sun was "birthed" in about 40 million to 50 million years, but its total evolution -- its whole life cycle -- will last more than 11 billion years.

When we look up into the dark night sky from the Earth's surface, we will always see the stars "twinkling." The Earth's atmosphere is constantly turbulent, with moving currents and varying densities due, primarily, to pockets of rising warm air and falling cooler air. As starlight passes through this turbulent air, it rapidly varies in its apparent brightness and position. The cumulative effect of these variations is what we see as "twinkling."

Arnold M. Heiser
Professor of physics and astronomy, emeritus

-- Compiled by Jessica Hathaway

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