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Cancer

Response to Treatment

The differences between tumor types often influence how well a tumor responds to anticancer drugs. Many anticancer drugs target the DNA of proliferating cells. This results in the paradox that rapidly growing tumors are more likely to be injured by chemotherapy. Interestingly, anticancer drugs often don't kill tumor cells outright: they damage a cell's DNA, and that damage triggers the cell to self-destruct through apoptosis.

Radiation therapy is also a powerful tool for treating cancer, but some types respond better than others. Leukemias generally respond extremely well to radiation. But radiation therapy by itself can seldom cure leukemia because the disease is spread throughout the body and the maximum dose a patient can tolerate is reached before the leukemia is eliminated.

Radiation therapy is also used to treat a variety of solid tumors. The chance that radiation will cure a solid tumor is best if the tumor is small. But the likelihood of catching it early, when it is small, often depends on which organ is affected, what symptoms it causes, and whether effective screening methods are available for detecting it.

 

 

Small tumors respond better to radiation therapy because once a tumor reaches a certain size, it develops regions of low oxygen. Hypoxia works against radiation therapy. If cells within a tumor are surviving under hypoxic conditions, it can take three times the amount of radiation to kill them than would be required for an oxygenated cell.

If that level of radiation is greater than the body can safely tolerate, then while radiation therapy might kill most of the cells in a large tumor, some cells would likely survive to become the seeds of the tumor's recurrence. Low oxygen levels protect tumor cells from radiation because oxygen must be present in the cell for radiation to effectively damage the cancer cell's DNA.

Some solid tumors, however, seem to have a general resistance to radiation therapy, yet differences between tumors can yield surprising results. Melanomas have a great reputation for not responding to radiation. And that's true for the majority of them, but sometimes they respond extremely well. Why malignant melanoma often doesn't but sometimes does respond well to radiation therapy isn't known yet.

Year by year, researchers are gaining a better understanding of how cancers are similar and how they differ. Such understanding provides the fertile soil from which new treatments grow.

Understanding the differences between cancers—the genetics and molecular mechanisms that regulate tumor cell growth—also presents new targets for interfering with the growth of tumor cells. When scientists discovered that estrogen receptors regulated the growth of a subtype of breast cancer (i.e., hormone-dependent breast cancer), they began developing drugs that specifically blocked the receptor, making it inaccessible to estrogen. Tamoxifen was the first of those drugs.

Knowledge of hormone dependency has made a real difference in the treatment of breast cancer.

Tamoxifen as therapy, and now as a chemopreventive agent, has very effectively extended disease-free survival time and overall survival time for women with hormone-dependent breast cancers. Following on the heels of that success is the development of new classes of drugs that are now becoming available. These include aromatase inhibitors, which lower estrogen levels in the body, and compounds known as selective estrogen-receptor modulators, or SERMs. These include the new drug raloxifene.

The differences in types of cancer have implications for patients in another way, as well. There's a culture of cancer around the world. Almost universally, the word 'cancer' is associated with images of suffering, malnourishment, and death.

But the differences between malignancies mean that the term cancer encompasses many different possibilities: some types are associated with serious problems, while others don't cause a lot of problems; they are treatable, even curable. Even patients with the same kind and stage of cancer may have different experiences: each disease is different, and each cancer in each individual is different. This should ease the fears of patients with treatable disease, and be a source for hope for those with more difficult disease.

This article originally appeared in Frontiers (Autumn 1998) a chronicle of cancer programs at The Ohio State University and was adapted for use on NetWellness with permission, 2004.

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Last Reviewed: Feb 21, 2005

Darrell E Ward, MS Darrell E Ward, MS
Associate Director
Cancer Communications
Wexner Medical Center
The Ohio State University

Robert W Brueggemeier, PhD Robert W Brueggemeier, PhD
Dean/Professor, Pharmacy Central Business Office
College of Pharmacy
The Ohio State University

Michael A Caligiuri, MD Michael A Caligiuri, MD
Professor of Hematology
Professor of Molecular Virology, Immunology, & Medical Genetics
College of Medicine
The Ohio State University

Reinhard A Gahbauer, MD Reinhard A Gahbauer, MD
Former Professor
The James
The Ohio State University

Eric H Kraut, MD Eric H Kraut, MD
Professor of Hematology
College of Medicine
The Ohio State University