Abstract
BackgroundIt is unclear whether estrogen receptor (ER)-status of first primary breast cancer is associated with risk of metachronous (non-simultaneous) contralateral breast cancer (CBC), and to what extent endocrine therapy affects this association.MethodsWe studied the effect of ER-status of the first cancer on the risk of CBC overall, and for different ER-subtypes of CBC, using a large, population-based cohort. The cohort consisted of all women diagnosed with breast cancer in the Stockholm region 1976–2005; 25715 patients, of whom 940 suffered CBC. The relative risk was analyzed mainly using standardized incidence ratios (SIR).ResultsWomen with breast cancer had a doubled risk of CBC compared to the risk of breast cancer in the general female population (SIR: 2.22 [2.08–2.36]), for women with a previous ER-positive cancer: SIR = 2.30 (95% CI:2.11–2.50) and for women with a previous ER-negative cancer: SIR = 2.17 (95% CI:1.82–2.55). The relative risk of ER-positive and ER-negative CBC was very similar for women with ER-positive first cancer (SIR = 2.02 [95%CI: 1.80–2.27] and SIR = 1.89 [95%CI: 1.46–2.41] respectively) while for patients with ER-negative first cancer the relative risk was significantly different (SIR = 1.27 [95% CI:0.94–1.68] for ER-positive CBC and SIR = 4.96 [95%CI:3.67–6.56] for ER-negative CBC). Patients with ER-positive first cancer who received hormone therapy still had a significantly higher risk of CBC than the risk of breast cancer for the general female population (SIR = 1.74 [95% CI:1.47–2.03]).ConclusionThe risk of CBC for a breast cancer patient is increased to about two-fold, compared to the risk of breast cancer in the general female population. This excess risk decreases, but does not disappear, with adjuvant endocrine therapy. Patients with ER-positive first cancers have an increased risk for CBC of both ER subtypes, while patients with ER-negative first cancer have a specifically increased risk of ER-negative CBC.
Highlights
Of all women with breast cancer, each year 0.6–0.7% will develop contralateral breast cancer (CBC) [1,2,3,4,5,6], translating into approximately 10–15% of all breast cancer patients being diagnosed with CBC during the first 20 years after initial diagnosis [4,7]
The overall 5-year incidence decreased from 533 cases per 100 000 PYR, for women diagnosed with their first cancer in 1976–1980 to 322 cases per 100 000 PYR for women diagnosed with their first cancer in 1996–2000
We found the risk of CBC for breast cancer patients to be about twice as high compared to the risk of breast cancer in the general female population, independently of estrogen receptor (ER)-status of the first cancer
Summary
Of all women with breast cancer, each year 0.6–0.7% will develop contralateral breast cancer (CBC) [1,2,3,4,5,6], translating into approximately 10–15% of all breast cancer patients being diagnosed with CBC during the first 20 years after initial diagnosis [4,7]. Estrogen receptor (ER) status acts both as a prognosticator, independent of treatment, and as a predictor of endocrine therapy response [13,14,15] It is still not clear how hormone receptor status of the first breast cancer affects the risk of CBC. We conducted a population-based analysis, contrasting the risk to develop CBC among breast cancer patients to the risk to develop breast cancer among the general female population. It is unclear whether estrogen receptor (ER)-status of first primary breast cancer is associated with risk of metachronous (non-simultaneous) contralateral breast cancer (CBC), and to what extent endocrine therapy affects this association
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