‘The best way to screen’

DBT with FFDM demonstrates increased rates in cancer detection compared with FFDM alone. Image comparison between 2-D, tomosynthesis and C-view synthetic 2-D.

Aiming to balance  the latest in cutting-edge science with everyday clinical practice,  this year’s ESOBI meeting featured a session entitled the ‘The best way  to screen’.  A timely debate in light of the new draft proposal for  European guidelines for breast cancer screening and diagnosis that is  open for feedback and also when ESOBI are promoting their latest  publication ‘Statement in favour of breast screening’.

Nationwide screening programmes result in substantial mortality reductions

Screening with mammography  alone is a cost-effective way to save lives. Throughout Europe a  substantial reduction in mortality from breast cancer can be seen in  those countries that have implemented nationwide screening programmes.  Interestingly, the shift from analogue to digital between 2005 and 2010  led to improved results and showed that more high-risk tumours are now  detected by mammography.

Of course, there remain drawbacks with  mammography screening, such as false positives and over diagnosis.  However, so far no other modality has proven to save lives and no  information is available regarding the aggressiveness of tumours  detected by other modalities, for example the positive predictive value  of ultrasound is substantially lower and quality control (operator  dependent) is difficult. 

For these reasons screening with mammography alone is still the gold standard for population-based screening programmes.

Nevertheless, even screening with full-field  digital mammography (FFDM) fails to detect 15-30% of cancers and in  women with dense breasts, approximately 7% of the 50-70-year-old  population, sensitivity for 2-D mammography can be as low as 58%. 

Digital Breast Tomosynthesis (DBT), a 3-D digital  mammography system, is a promising tool for improving screening in  these women. After X-ray acquisition of a series of 2-D images  (projections), reconstruction of the breast is done at different heights  above the detector. Current DBT systems are commercialised by five  different manufacturers and are routinely used in radiology centres and  in several countries, the technique has approval for screening and  diagnostics.

Comparison of DBT with FFDM favours DBT

DBT has the potential to  improve cancer detection rates with only a small increase in radiation  dose. Retrospective reading studies comparing DBT with FFDM have shown  improvement in both sensitivity and specificity with DBT. Diagnostic  accuracy appears to be largely independent of breast density although  benefit appears greater in women with denser breasts. Results are less  clear regarding the detection of microcalcification and most studies  have found little improvement over 2-D mammography in the detection of  ductal carcinoma in situ (DCIS).

Used together in prospective screening studies,  DBT with FFDM has demonstrated increased rates in cancer detection  compared with FFDM alone. A reduction in false-positive recall rates has  also been shown in nearly all studies.

Several DBT issues must now be resolved

Screening with the addition  of DBT would approximately double the radiation dose received; but a  simulated FFDM image can be generated from a DBT scan. The combination  of simulated FFDM images and DBT is being evaluated within several  studies and some positive results have been published.

However, before this becomes a realistic  proposition for widespread screening programmes several issues around  DBT need to be resolved, not least the wide range of totally different  characteristics in the machines (angular range, scanning angle,  filter/target combination, tube motion, etc.), and the use of different  reconstruction methods: filtered back projection or iterative  reconstruction. 

Also, the additional reading time, the large IT  storage, connectivity problems and over diagnosis of low grade cancers  will all need to be correctly modelled to obtain cost-effectiveness  similar to that of current screening if the addition of DBT is to become  a way to improve breast cancer screening.

04.08.2017

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