According to the definition provided by the European guidelines, the case of the tumor described by Dr Weth is that of a typical interval cancer. The tumor was diagnosed outside the cancer screening program after a negative screening result and before the next regular screening round, and the cancer did not have a visible correlate in the obtained mammogram even when this was re-analyzed. In terms of its categorization, this is therefore a genuine interval cancer. The assumption that the tumor must have been present at the time of the screening examination, and at a size that would have been detectable by ultrasound, is speculation.
A current ultrasound study from the national mammography screening program shows that when larger numbers of cases are studied (n=2803), the detection of additional breast cancers in the course of diagnostic evaluation using systematic bilateral ultrasound is low, at 0.21% (6/2803) (1), even though individual cases of breast cancer have been diagnosed by ultrasonography after a negative screening mammogram.
We are currently preparing a publication that deals, among other issues, with the distribution of different histological subtypes of breast cancer, relative to the modality of their detection. We agree with Dr Weth that invasive lobular cancers (ILC) account for some 20% of cases. Before mammography screening was introduced, the proportion of women aged 50–69 years in North Rhine–Westphalia (NRW) was 19.2%. By comparison, of the tumors detected by screening, ILC accounted only for a slightly lower proportion, and this is not fundamentally different for interval cancers. If digital mammography, as used in NRW, were a limited modality by which to detect ILC—especially in patients with dense breast tissues—then this tumor type would have to be clearly overrepresented among interval cancers. This, however, is certainly not the case.
Footnotes
Conflict of interest statement
Dr. Heidinger is managing director of the Epidemiological Cancer Registry North Rhine–Westphalia (Epidemiologisches Krebsregister NRW GmbH). Dipl.-Soz. Batzler and Dr. Krieg are employees of the registry.
Dr. med. Weigel is a scientific employee of the Westphalia Wilhelm University of Münster, specializing in medicine. Her duties include scientific research and teaching, for example for the Mammography Reference Centre, a third party-funded project at Münster University Hospital.
Until his death, Dr. rer. nat. Biesheuvel worked as an epidemiologist for the Mammography Reference Centre, a third party-funded project at Münster University Hospital.
Prof. Dr. med. Heindel runs the Mammography Reference Centre, a third party-funded project at Münster University Hospital. He manages other third-party funding for research projects into breast cancer screening of the EU (High Resolution X–Ray Imaging for Improved Detection and Diagnosis of Breast Cancer [HighRex], EU project contract no. 037642) and the German Federal Office for Radiation Protection (BfS, Bundesamt für Strahlenschutz).
Prof. Dr. Hense manages third-party funding of the German Federal Office for Radiation Protection (BfS, Bundesamt für Strahlenschutz) for research projects into breast cancer screening.
All authors except Dr. Krieg were/are speakers for UKM Akademie GmbH at continuing professional development events on the qualification, ongoing training, and further professional development of mammography screening program doctors and radiologists and receive payment for their work.
References
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