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Incidence and Prognosis of Synchronous and Metachronous Bilateral Breast Cancer

Mikael Hartman, Kamila Czene, Marie Reilly, Jan Adolfsson, Jonas Bergh, Hans-Olov Adami, Paul W. Dickman, Per Hall

From the Department of Medical Epidemiology and Biostatistics, Stockholm Söder Hospital and Oncologic Center, Clintec, and Department of Oncology, Radiumhemmet, Karolinska Institutet and Karolinska University Hospital, Stockholm, Sweden; and the Department of Epidemiology, Harvard University, Boston, MA

Address reprint requests to Mikael Hartman, MD, Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, PO Box 281, 171 77 Stockholm, Sweden; e-mail: Mikael.Hartman{at}ki.se

Purpose: Because the incidence of breast cancer is increasing and prognosis is improving, a growing number of women are at risk of developing bilateral disease. Little is known, however, about incidence trends and prognostic features of bilateral breast cancer.

Patients and Methods: Among 123,757 women with a primary breast cancer diagnosed in Sweden from 1970 to 2000, a total of 6,550 developed bilateral breast cancer. We separated synchronous (diagnosed within 3 months after a first breast cancer) and metachronous bilateral cancer, and analyzed incidence and mortality rates of breast cancer using Poisson regression models.

Results: The incidence of synchronous breast cancer increased by age and by 40% during the 1970s, whereas the incidence of metachronous cancer decreased by age and by approximately 30% since the early 1980s, most likely due to increasing use of adjuvant therapy. Women who developed bilateral cancer within 5 years and at age younger than 50 years were 3.9 times (95% CI, 3.5 to 4.5) more likely to die as a result of breast cancer than women with unilateral cancer. Women with a bilateral cancer diagnosed more than 10 years after the first cancer had a prognosis similar to that of a unilateral breast cancer. Adjuvant chemotherapy of primary cancer is a predictor of poor survival after diagnosis of early metachronous cancers.

Conclusion: We found profound differences in the incidence trends and prognostic outlook between synchronous and metachronous bilateral breast cancer diagnosed at different ages. Adjuvant chemotherapy therapy has a dual effect on metachronous cancer: it reduces the risk, while at the same time it seems to worsen the prognosis.

Supported by US Army Grant No. DAMD 17-03-1-1-0771.

Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.