U.S., Soviets Plan Study of Breast Cancer Prevention : Medicine: An anti-estrogen drug would be used. The project would involve 20,000 women.

American and Soviet cancer specialists signed an agreement here Thursday for a 10-year, $100-million study of 20,000 women in the two countries to determine whether a hormonal treatment can prevent breast cancer.

Dr. Phillip D. Bretz, director of the Desert Breast Institute in Rancho Mirage, Calif., said that women thought to be most likely to develop breast cancer would be given tamoxifen, an anti-estrogen drug, and then be closely monitored by breast cancer specialists to see whether the drug could be used in preventive treatment.

“Tamoxifen appears to be both the most promising and safest of all the drugs we know about for the prevention of breast cancer,” Bretz said. “In the United States, the Soviet Union and in many industrialized countries, breast cancer is the most prevalent cancer among women.”

Tamoxifen, which is manufactured by the British firm Imperial Chemical Industries and sold under the brand name Nolvadex, has been used with considerable success for 11 years in the post-surgical treatment of breast cancer patients to prevent a recurrence, Bretz said.

The proposed study is the first undertaken on such a scale jointly in the United States and the Soviet Union. The patients, about 10,000 each from the Soviet Union and the United States, will primarily be the daughters, sisters or mothers of women who have had breast cancer and thus are regarded as the most likely to develop cancer themselves.

The treatment involves taking two tablets a day. The researchers said that tamoxifen has minimal negative side effects and often reduces cholesterol and eases cardiovascular problems.

Tamoxifen works by blocking so-called estrogen receptors--areas on the surface of cells to which the hormone binds to exert its effects. In that way, it blocks the effects of estrogen, which plays a role in the development and progression of breast cancer.

Soviet women who were exposed to large amounts of radiation after the nuclear accident at Chernobyl in April, 1986, will also be included in the study, with the hope of preventing the development of breast cancer among them, according to Dr. David Zaridze, deputy director of the All-Union Cancer Research Institute in Moscow.

A new blood test, developed by Dr. Adeline Hackett of the Aeron Corp. of Oakland, Calif., and researchers at UC Berkeley is being used in the Ukrainian capital of Kiev, where many of the Chernobyl victims are treated, to measure the amount of radiation absorbed by each woman.

“We know that radiation is carcinogenic for humans, but we do not know how carcinogenic--that is, how much radiation is likely to increase the risk of various cancers and leukemias,” Zaridze said. “In Hiroshima and Nagasaki (on which atomic bombs were dropped in World War II), there was an increase in all cancers and leukemias, but only about 300 cases of solid tumors and the same number of leukemias were directly attributed to radiation. We need to know more about how radiation causes tumors, and with this blood test we believe we can.”

Another blood test, also developed by Hackett, will be used to assess the level of tamoxifen in each woman’s body and her response to the drug.

The tamoxifen study must still be approved by the U.S. Food and Drug Administration, which will hold an open hearing in Washington next month on the proposed scope and method of the research, but the U.S. researchers expressed confidence that the project would be approved and fully under way by the end of the year.

Bretz said he expects the study’s $100-million cost to be financed primarily with grants from the U.S. and Soviet governments and by pharmaceutical companies.

The project will be coordinated in the United States by Bretz and Dr. Philip B. Dreisbach of the Eisenhower Medical Center in Rancho Mirage and in the Soviet Union by Zaridze at the national Cancer Research Center and carried out in various cities in each country.

“This drug has already proven to work in sustaining the post-operative remission in women who have had breast cancer and in preventing the spread of cancer to the other breast,” Dreisbach said. “The time has come to determine whether it can prevent breast cancer.”

In cases where breast cancer does develop among Soviet women, the project will also include the use of early laser surgery rather than radical surgery, radiation or chemotherapy, Bretz said.

Times staff writer Janny Scott, in Los Angeles, contributed to this story.