Many women with a noninvasive form of breast cancer have chosen in recent years to undergo only surgery. Radiation was not necessary, they were told. That advice may have been wrong.

A Harvard University study of women with ductal carcinoma in situ (small tumors of the milk ducts) has found a “surprisingly high rate of recurrence” among a small group of patients who opted for surgery alone.

The finding suggests that all such patients — 50,000 are diagnosed annually in the United States — should consider additional treatment with radiation. About a third of women with the form of breast cancer, called DCIS, are treated solely with surgical removal, most often breast-preserving lumpectomy, federal data show.

Based on the new findings, Harvard-affiliated hospitals are routinely giving radiation therapy to DCIS patients, said senior study author Dr. Jay R. Harris, chief of radiation oncology at Dana-Farber Cancer Institute and Harvard Medical School in Boston.

It’s unclear how the study results will affect decision-making elsewhere.