In Australia, women still present with large breast cancers despite the introduction of mammography screening there in 1991, researchers report in the International Journal of Cancer.

“Our study suggests that greater participation (in mammography screening) could help some women avoid diagnosis with a large breast cancer,” Dr. Anne Kricker from the University of Sydney and colleagues conclude.

Until now, no study has comprehensively examined potential contributors to the persistence of large breast cancers in populations where screening is offered, the note.

To investigate, Kricker’s team interviewed 1459 women about their personal, mammogram, and breast histories in the years before diagnosis of breast cancer. They also collected biological characteristics of breast tumors and mammogram dates from medical records.

Just over half of the women, 766, had tumors measuring 2 centimeters or greater and, according to the team, the biggest factor influencing breast cancer size at diagnosis was the method of detection.

The likelihood of a large breast tumor (greater than 2 centimeters) was substantially lower for detection by a screening mammogram than for detection after a breast symptom, Kricker and colleagues found.

The odds of having a large breast cancer with mammogram detection were lower for women aged 55 to 69 years than for women 40 to 54 years old and were lower for postmenopausal women than for premenopausal women.

Being overweight and having a more aggressive tumor were two factors significantly associated with higher odds of a larger cancer being detected, the investigators say. This was true for mammography-detected and symptom-detected breast cancers.

In this study, the “most important factors” in being diagnosed with a large breast cancer were related to the health system (detection method), the cancer (grade), and the women (being overweight), the study team notes.

Of these, detection method (mammography) and being overweight “are the most amenable to intervention.”

“Although women need to be aware of the potential harms of screening, our study suggests that greater participation could help some women avoid diagnosis with a large breast cancer,” they conclude.

SOURCE: International Journal of Cancer, December 15, 2008.