Clinical characteristics and the associated risk factors of the development of bilateral breast cancers: A case-control study

Background: The clinical impacts of bilateralism on prognosis and clinical decision-making remain contradictory
particularly in areas with low incidence and delayed diagnosis of primary breast cancer. Identification of women
at risk of bilateral breast cancer is required to improve patient management and to design the appropriate
surveillance.
Methods: A total of 1083 women were enrolled and analyzed for the presence of synchronous and metachronous
bilateral breast cancer as cases and unilateral breast cancer as controls during the median follow-up of 4.8 years.
Results: The incidence of bilateral breast cancer was 7.5% (81 of 1083). In comparison with unilateral breast
cancers, bilateral cases were significantly diagnosed in younger women (P = 0.037, mean age was 35.6 years)
who had a larger tumor size (P = 0.012, mean tumor size was 8 cm in diameter). Histological type of lobular
cancer was identified as one of the risk factors for the development of contralateral breast cancer (OR 5.564, 95%
CI: 3.219–9.620) and synchronous bilateral breast cancer (OR 2.561, 95% CI: 1.182–5.550). Bilateral breast
cancer had significantly shorter progression-free survival (Mean survival was 26.6 vs 52.5 months for bilateral
and unilateral breast cancers, respectively; P = 0.001) and shorter time to develop distant metastasis (Mean
survival was 41.7 vs 104 months for bilateral and unilateral breast cancers, respectively; P = 0.001).
Conclusion: Patients with first primary breast tumors with lobular histological type and advanced stages were
observed to have higher risks for the development of contralateral breast cancers