Deccan Herald » Science & Technology » Detailed Story

Mammography better prognosis for breast cancer

Reuters

Mammography can detect tumours that are both slower growing and less biologically lethal than those found symptomatically.

Breast cancer detected by screening mammography (breast imaging) had a significantly better prognosis even after its spreading to lymph nodes than the disease found utilising other technology, a new study conducted on 150,000 women says.

A likely reason for this finding is that mammography can detect tumours that are both slower growing and less biologically lethal than those found symptomatically, the researchers of University of Texas' M D Anderson Cancer Centre, in an article published in 'Journal of Nations Cancer Institute,' said.

"The study is important because the survival benefit seen in this analysis is much greater than one would expect for screen-detected breast cancer," the study's lead author Donald Berry, chair of the Department of Biostatistics and Applied Mathematics, said.

Based on the results, Berry suggested that method of detection should be considered when a treatment plan for newly diagnosed breast cancer is being devised and that this information also should be collected by researchers conducting clinical trials of experimental therapeutic strategies.

"Of two women who have the same age, size of tumours, and similar stage of cancer and spread to lymph nodes, the one whose cancer was detected with mammography has a reason to be happier than the woman whose cancer was detected symptomatically," Berry said.

While that sounds like good news for some patients, Berry says the conclusion should not be over interpreted.

Study methodology

In this study, researchers examined data from three large randomised breast cancer screening trials the Health Insurance Plan (HIP) of New York, which assigned about 62,000 women to screening or to a control group and two Canadian National Breast Cancer Screening Studies (NBSS), which included a total of 44,790 women in the screening groups and 44,961 women in the control groups.

They then looked only at women in these studies who were eventually diagnosed with breast cancer and adjusted for stage and other tumour characteristics as a way to eliminate what is known as "lead-time bias."

Lead time is the time between when the tumour was detected by mammography and when the tumour would have been detected in the absence of screening. Lead-time bias occurs because lead time is added to the survival time of women detected by mammography but not to women whose tumours are detected clinically, Berry said.

If lead-time bias was responsible for improved survival and if it was eliminated from the screening mammography group, then those patients should have the same survival, statistically, as women whose cancer was detected outside of mammography, the researchers said. But what they found is different.

They discovered that all things being equal, the method of detection was a statistically significant independent predictor of breast cancer survival. After adjusting for stage of disease, patients whose breast tumours were discovered after a previous negative mammography screen had a 53 per cent greater risk of death from the cancer than women with screen-detected cancer. Patients in the control group (where no mammography was used) had a 36 per cent increased risk of death compared to screened patients.

"What is new here is that we found an effect that is beyond stage shift," Berry said.