Gene therapy may increase cancer cure rates, medical physicists show

An innovative combination of two medical procedures-gene therapy and radiation therapy–can increase cancer cure rates by significant amounts compared to the cure rates offered by conventional radiation therapy alone, a Virginia Commonwealth University (VCU) team has concluded. The researchers presented their results last month in Montreal at the annual conference of the American Association of Physicists in Medicine.

Known as genetic radiotherapy, the combined treatment can potentially increase cancer cure rates by up to 70% over present therapies that exclusively use radiation therapy, the researchers say. The combined technique is currently evolving from laboratory studies to human clinical trials.

In genetic radiotherapy, cancer cells are infected with a virus that makes tumor cells more sensitive to–and more easily destroyed by–radiation such as x-rays. At last month’s medical physics meeting, the VCU researchers presented a quantitative model predicting the increase in cancer cure rates with genetic radiotherapy.

“Our model incorporates human patient data from large radiotherapy clinical trials as well as experimental genetic therapy data from laboratory work,” says Dr. Paul Keall, an assistant professor in VCU’s radiation oncology department.

To calculate the projected cure rates, the group considers the fraction of tumor cells that are genetically modified, or “transduced,” by the injected virus. They also consider the sensitivity of the genetically transformed cells to radiation.

With present laboratory technology, the researchers predict an increase in cure rate of 15% when genetic radiotherapy is used instead of conventional radiation treatments on non-genetically-altered cancer cells. Exploring an ideal situation in which all of the cancer cells are genetically modified, they find the technique can theoretically increase the cancer cure rate by as much as 70%. In their model, a “cure” means a lack of tumor recurrence at the site where the tumor was treated.

“Thus, our results indicate that genetic radiotherapy has the potential to significantly improve cancer cure rates compared to current radiotherapy practices,” says Keall. “Needed now are carefully controlled studies to test our predictions.”

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Meeting paper: “Radiobiological Predictions for Genetically Radiosensitized Tumors,” by Paul Keall, PhD Guido Lammering, MD, Theodore Chung, MD, and Rupert Schmidt-Ullrich, MD, all at Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA, USA, paper MO-E-517B-7, Monday, July 15, 2002, 44th Annual AAPM Meeting, Montreal, Quebec.