The modern approach is to cut out obvious tumors — because lumps big enough to detect may be too dense for drugs and radiation to destroy — and to use radiation and chemotherapy to wipe out microscopic disease in other places.

But doctors have continued to think that even microscopic disease in the lymph nodes should be cut out to improve the odds of survival. And until recently, they counted cancerous lymph nodes to gauge the severity of the disease and choose chemotherapy. But now the number is not so often used to determine drug treatment, doctors say. What matters more is whether the disease has reached any nodes at all. If any are positive, the disease could become deadly. Chemotherapy is recommended, and the drugs are the same, no matter how many nodes are involved.

The new results do not apply to all patients, only to women whose disease and treatment meet the criteria in the study.

The tumors were early, at clinical stage T1 or T2, meaning less than two inches across. Biopsies of one or two armpit nodes had found cancer, but the nodes were not enlarged enough to be felt during an exam, and the cancer had not spread anywhere else. The women had lumpectomies, and most also had radiation to the entire breast, and chemotherapy or hormone-blocking drugs, or both.

The study, at 115 medical centers, included 891 patients. Their median age was in the mid-50s, and they were followed for a median of 6.3 years.

After the initial node biopsy, the women were assigned at random to have 10 or more additional nodes removed, or to leave the nodes alone. In 27 percent of the women who had additional nodes removed, those nodes were cancerous. But over time, the two groups had no difference in survival: more than 90 percent survived at least five years. Recurrence rates in the armpit were also similar, less than 1 percent. If breast cancer is going to recur under the arm, it tends to do so early, so the follow-up period was long enough, the researchers said.