Finding a lump - even a benign one - during a breast self-examination is so traumatic for some women, they are three times more likely to stop checking than women who have never found a lump, a study says.

"On the other hand, women who have had a lump discovered through the health-care system - through a physician, a nurse or a mammogram - are twice as likely to begin (self-examinations) than women who never had a lump," said Nancy K. Janz, a researcher at the University of Michigan School of Public Health.Breast cancer affects about one in 10 women. It rarely occurs in men.

More than 80 percent of breast lumps are benign, according to the National Alliance of Breast Cancer Organizations. Most irregularities are found by women themselves, but researchers say only about 30 percent of women perform self-exams.

Janz and Marshall H. Becker, a professor of health behavior and education, studied the breast self-examination practices of 655 women: 179 with a lump discovered either through mammography or by a doctor or nurse; 83 with a lump they found themselves; and 393 with no history of breast lumps.

The findings, published recently in the American Journal of Preventative Medicine, showed that the discovery of a suspicious lump led to changes in the regularity of self-exams.

Among the self-discovery group, 17.1 percent checked themselves less frequently, compared with 5.4 percent in the control group and 8.5 percent in the health care-discovered group.

The stress, discomfort and cost of a biopsy, even when results show the lump isn't cancerous, makes some women view the process as being caused unnecessarily by the self-examination, the study said.

At the same time, 31.8 percent of the health care-discovered women started conducting self-exams more often, while increases were noted in 13 percent of the control group and in 11 percent of the women who found lumps themselves.

Among the findings:

- Confidence in being able to do a breast self-examination properly helped determine how regularly a woman practiced it.

- Smokers are more likely to perform regular self-exams. "It is possible that smokers perceive themselves at higher risk for cancer and thus adhere to recommended early screening techniques," the researchers said.

- Women who do not get yearly pelvic exams are less likely to practice regular breast self-examinations.