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. 2019 Apr;120(7):761-767.
doi: 10.1038/s41416-019-0403-z. Epub 2019 Feb 26.

Breast Cancer Mortality in Synchronous Bilateral Breast Cancer Patients

Free PMC article

Breast Cancer Mortality in Synchronous Bilateral Breast Cancer Patients

Mathias Kvist Mejdahl et al. Br J Cancer. .
Free PMC article


Background: Evidence suggests that patients with synchronous bilateral breast cancer (SBBC), diagnosed within 4 months, have an inferior prognosis compared to unilateral breast cancer (UBC) patients. Using data from nationwide Danish clinical databases, this cohort study investigated whether the inferior prognosis could be explained by SBBC patients having a more aggressive disease, or whether the prognosis could be explained by the fact that they have two simultaneous cancers.

Methods: Patients were diagnosed from 1999-2015. The main outcome was excess mortality, subtracting background population mortality from observed mortality. Differences between SBBC and UBC patients were evaluated by rate ratios (RR) and estimated by Poisson regression.

Results: In total, 1214 SBBC and 59 177 UBC patients were included. SBBC patients had a significantly higher excess mortality than UBC patients after adjustment for age and period (RR = 1.73; 95% CI:1.44-2.08; p < 0.01) and after adjusting for characteristics of the worst tumour as traditionally done (RR = 1.31; 95% CI:1.08-1.57; p = 0.01). However, adjusting for characteristics of both tumours, using a more advanced competing risks model, no difference was observed (RR = 1.01; 95% CI:0.83-1.22; p = 0.93).

Conclusions: Our study does not support that the inferior prognosis in SBBC patients is due to having more aggressive tumours per se, but rather the combined effect of having two simultaneous cancers.

Conflict of interest statement

The authors declare no competing interests.


Fig. 1
Fig. 1
Flow chart. DBCG Danish Breast Cancer Group, DCIS ductal carcinoma in situ, LCIS lobular carcinoma in situ, SBBC synchronous bilateral breast cancer, UBC unilateral breast cancer
Fig. 2
Fig. 2
Observed cumulative mortality rates of synchronous bilateral (formula image) and unilateral (formula image) breast cancer patients
Fig. 3
Fig. 3
Observed and predicted cumulative mortality rates (CMR) of synchronous bilateral breast cancer patients. a Predicted rates based on characteristics of the worst tumour: Observed CMR (formula image), Predicted CMR due to characteristics of the worst tumour (+ expected) (formula image), and expected background CMR (formula image). b Predicted rates based on the characteristics of both tumours: Observed CMR (formula image), Predicted CMR due to left tumour (+ expected + right) (formula image), Predicted CMR due to right tumour (+ expected) (formula image), and expected background CMR (formula image)

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