SAN DIEGO — Giving women chemotherapy for early breast cancer may protect them from getting entirely new kinds of cancer many years later, according to a study reported Monday.

The study, conducted in Sweden, found a significant reduction in the development of a variety of new tumors, especially cervical cancer, after drug treatment for breast cancer.

Researchers theorized that the cancer-killing drugs may wipe out minuscule clumps of tumor cells throughout the body long before they can be found.

“Adjuvent chemotherapy may protect against the development of new primary cancers, at least in the first 10 years” after treatment, said Dr. Rodrigo Arriagada of Gustave-Roussy Institute in Villejuif, France.

Arriagada conducted the study with researchers from Karolinska Hospital in Stockholm and presented his results at a meeting of the American Society of Clinical Oncology.

Dr. Victor G. Vogel of M.D. Anderson Cancer Center in Houston said, “One could hypothesize that there are emerging tumors that, if exposed to chemotherapy, could be interrupted at an early stage.”

However, Dr. Bernard Fisher of the University of Pittsburgh said U.S. studies of women getting chemotherapy for breast cancer have shown no reduction in other cancers.

In the Swedish study, doctors compared 1,113 women with breast tumors that were more than 3 centimeters in size but hadn’t spread. They received either a three-drug combination of chemotherapy or radiation treatment for their early-stage breast cancer.

After 10 years of followup, 1 percent of the chemotherapy patients had gotten new cancers unrelated to their breast cancer, compared with 6 percent in the radiation group.

Arriagada said he believed the lower rate resulted from a truly protective effect of the chemotherapy, rather than from radiation causing more cancer in the other women.

Doctors generally agree that premenopausal breast cancer patients should get chemotherapy, as should older women whose cancers have spread substantially to their lymph nodes.

The study was started to see if chemotherapy and another common breast cancer treatment, the drug tamoxifen, increased the risk of some kinds of cancer.

Another phase of his study found hints — but no proof — of a possible adverse effect of tamoxifen, an estrogen-blocking drug used to prevent recurrence of breast cancer.

Among 2,365 breast cancer patients studied, 8 percent receiving tamoxifen developed new tumors, compared with 5 percent who did not take tamoxifen.