TUESDAY, May 3 (HealthDay News) -- Breast tumors that are detected in between regular screening mammograms tend to be more aggressive and fast-moving than those found during scheduled screenings, indicating that better screening methods are needed, researchers say.
"We may have to look at other imaging techniques or newer technologies to find these types of cancers," said Anna M. Chiarelli, co-author of a study published online May 3 in the Journal of the National Cancer Institute.
Other studies have come up with similar results but they didn't make a distinction between what these authors call "true" interval cancers, meaning those that weren't detectable by a radiologist on a regular screening mammogram but showed up in retrospect, as opposed to "missed" interval cancers, which did show on the previous mammogram but were missed.
"Interval cancers are a heterogeneous group," said Chiarelli, a senior scientist in prevention and cancer control at Cancer Care Ontario in Toronto, Canada. "We wanted to see the different pathologies [and] prognostic factors."
In this study, an interval cancer was one that was diagnosed within two years after the last negative mammogram.
The authors identified "true" interval cancers and "missed" interval cancers in a group of almost 431,500 Ontario women aged 50 or older who were screened from 1994 through 2002.
They then compared those tumors with a control group of mammography-detected cancers.
Both the true and missed interval cancers were more aggressive than the cancers picked up by screening in that they were a higher stage and grade.
But the true interval cancers had even more worrying characteristics -- they were three times more likely to have a high "mitotic index," which is a measure of how fast the cells are dividing. They were also more than twice as likely to be both estrogen-receptor and pr
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