Breast cancer

More evidence supports tomosynthesis for breast cancer screening

Digital breast tomosynthesis plus synthesised 2D (s2D) mammography – colloquially called 3D mammography – significantly increases the detection rate for invasive breast cancer over the current breast screening standard of digital mammography.

According to a German study of 99,689 women randomly assigned to digital breast tomosynthesis plus s2D mammography or digital mammography, the detection rate of invasive breast cancers was 48% higher in the tomosynthesis group (7.1 v 4.8 cases per 1,000 women screened; HR 1.48).

“The invasive cancer detection rate for breast cancers with tumour size pT1 was substantially higher in the digital breast tomosynthesis plus s2D mammography group than the digital mammography group (OR 1·73 [95% CI 1·41–2·13]).”

The study, published in The Lancet Oncology, found no marked differences in the detection rate of DCIS between the groups (OR 0·94).

Recall rates were similar in both groups (OR 0.98) although the positive predictive value of recall (PPV1) was higher in the digital breast tomosynthesis plus s2D mammography group (OR 1.50).

“A higher PPV1 on the basis of a higher invasive cancer detection rate with digital breast tomosynthesis plus s2D mammography than digital mammography presents a desirable screening performance,” the study said.

An extended follow-up phase of the study will provide interval cancer rates in both groups.

An accompanying Comment article authored by Professor Nehmat Houssami from the University of Sydney, said interval breast cancer and advanced cancer rates at subsequent screening rounds were required as intermediate surrogates for screening effectiveness.

“A reduction in interval breast cancer rates and advanced cancer rates would suggest a beneficial effect on progressive cancers, also indicating that tomosynthesis does not preferentially increase overdiagnosis,” she said.

“A reduction in rates of interval cancers following the increased cancer detection rate of the magnitude achieved with tomosynthesis screening would provide crucial evidence that this enhanced screen-detection was identifying cancers that would have clinically progressed within 2 years of screening, ultimately extending the mortality benefit from breast screening.”

Professor Houssami said without that evidence, there was the concern that replacing mammography with tomosynthesis would lead to overdetection and overdiagnosis.

However other factors such as a reduced recall rate were already driving a shift to the new technology, particularly in the US.

“Strategically, population-based breast screening programmes need to proactively prepare for the possibility of a transition to tomosynthesis through programme-embedded trials to accelerate evidence on key screening outcomes, and to identify the most appropriate model to use tomosynthesis, which might entail novel screen-reading approaches and adaption of the double-reading process,” she said.

As a measure of safety, the German study found median glandular radiation dose was higher in the tomosynthesis group (1·86  v 1·36 mGy) but still under their national diagnostic reference level of 2·0 mGy.

Professor Houssami has previously led a pilot screening study in Australia which found more breast cancers were detected by tomosynthesis than standard mammography.

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