Synchronous bilateral breast cancer (SBBC): Concordance of receptor status between right and left breast.

Abstract

572 Background: This analysis was prompted by a patient who presented with SBBC who had and ER+, HER2- cancer in one breast and an ER-, HER2+ cancer in the other. Since both breasts have the same genetic background and environmental exposures, concordance should be virtually identical unless other factors are at play. Methods: SBBC was defined as bilateral cancer diagnosed concurrently or within 6 months of each other. Cases were identified retrospectively from patients seen at Rush University Medical Center. This analysis was limited to invasive SBCC (ISBBC). Estrogen receptor (ER) and Her2/neu (HER2) status were assessed according current ASCO/CAP guidelines. Correlation between ER and HER2 status was determined using κ statistic. Results: From January 1998 to December 2012, 33 cases of ISBBC were diagnosed. In 65% of cases synchronous disease was diagnosed concurrently. The average age at diagnosis was 56. The majority were multiparous and 79% post menopausal. About half of the patients (55%) had at least one first degree relative with a history of breast or ovarian cancer and 9% of the cohort had a deleterious mutation in BRCA1 or BRCA2. Infiltrating ductal was most common (74%) followed by infiltrating lobular (21%). 53% of breasts specimens also contained ductal carcinoma in situ. 68% of tumors were ER positive and 8% were HER2 positive. Concordance in ER status was seen in 73% of cases (kappa coefficient 0.14) and in HER2 status was 64% (Kappa coefficient 0.35). Conclusions: Despite identical hereditary and environmental exposure, some patients develop ISBBC cancers with discordant receptor status. While this is the exception, it suggests that other factors influence important tumor characteristics. [Table: see text]