Interval breast cancers have worse tumor characteristics and survival compared to screen-detected breast cancers

Background There is debate to what extend screen-detected cancers (SDC) differ in tumor characteristics and survival from tumors that are detected not trough screening. These can be divide into three groups. Firstly, tumors who manifest clinically in the period between two screens after a negative screening (interval cancers) within 12 months or, secondly, within 12-24 months. Thirdly, we identified tumors in patients with a positive screening, followed by a benign assessment in the hospital, who developed breast cancer 12-24 months after screening (IC-after-positive-screen). The aim of this study was to determine whether interval cancers and IC-after-positive-screen have worse tumor characteristics and survival compared to SDC. Regarding decision-making for more aggressive treatment, these data are essential. Methods All women (50-75) who underwent a screening by the Dutch National Screening Program, region North between 2004-2008 were selected and data were merged with the Netherlands Cancer Registry. SDC (diagnosed <12 months after positive screening), interval cancers diagnosed <12 months after negative screening (IC<12) or 12-24 months after negative screening (IC12-24), and IC-after-positive-screen were identified. Tumor characteristics of each group were compared to SDC using chi2. Differences in survival were analyzed with multivariable Cox regression, corrected for differences in tumor characteristics. Results In total 4,472 patients were included, 3,363 SDC, 501 IC<12m, 861 IC12-24m and 48 IC-after-positive-screen. Of all SDC, 14% were diagnosed as in situ cancers. A lower percentage of in situ cancers was diagnosed in IC<12m and IC12-24m (6% and 4%, respectively; p<0.001). In situ cancers were diagnosed in 15% of IC-after-positive-screen. Compared to SDC, invasive IC<12m and IC12-24m were more often poorly differentiated (p<0.001), larger than 2 cm (p<0.001), and had more often positive lymph nodes (p<0.001) or metastasis (p<0.001; Table 1). Furthermore, invasive IC<12m and IC12-24m were less often of the ductal type (p=0.002) or hormone receptor positive (p<0.001), compared to SDC. IC-after-positive-screen were not statistically significant different from SDC for all these factors. In total 608 (13%) women died. No difference in survival was found for IC<12m (HR=0.86, 95%CI=0.66-1.12) and IC-after-positive-screen (HR=1.40, 95%CI=0.58-3.39) compared to SDC. Women with an IC12-24m had a worse survival than SDC (HR=1.44, 95%CI=1.17-1.77). Conclusions IC<12m and IC12-24m had less favorable characteristics than SDC. IC-after-positive-screen had similar characteristics and have a similar prognosis as SDC. However, as the number of IC-after-positive-screen was small, this should be part of further research. Women with an IC12-24 had worse survival compared to SDC.