Chicago ? Doctors reading mammograms miss an average of 2 in every 10 cases of breast cancer, even for women with lumps and other symptoms, researchers reported Tuesday.

In a stark reminder of the limitation of the common diagnostic test, the researchers found wide variation in radiologists’ ability to detect cancer in breast X-rays, with some missing as many as 7 out of 10 cases. In other words, the test’s ability to detect cancer is strongly dependent on who is reading it.

“Women think mammography is perfect, so if they get a negative (normal) mammogram, they think they’re safe for at least the next year,” said Diana Miglioretti, lead author of the study, which appears in this week’s Journal of the National Cancer Institute. “The reality is, they shouldn’t be falsely reassured by a negative mammogram.”

That message was seconded by Dr. Leonard Berlin, chief of radiology at Rush North Shore Medical Center in north suburban Skokie, Ill., who was not involved in the study.

“You can have cancer and still have a normal mammogram,” Berlin said. “If you have any sign or symptom, you need to pursue it. That’s the bottom line.”