Abstract P4-09-26: The difference between metachronous and synchronous bilateral breast cancer in terms of clinical features and biology
Authors: Arima N , Nishimura R , Osako T , Nishiyama Y , Fujisue M , Okumura Y , Murakami K , Toyozumi Y 
Published: May 2016

Abstract
Introduction
The recent diagnostic modality such as MRI can diagnose a tiny breast lesion even in healthy contralateral breasts. Recently, the rate of contralateral prophylactic mastectomy (CPM) is on the rise in the United States. In Japan, the CPM has been started for selected patients with a high risk. In this study, we divided bilateral breast cancers into the synchronous and the metachronous group and then compared the clinical features and biology.
Patients and Methods
Out of 216 bilateral breast cancer patients who underwent surgery between 1995 and March 2015, there were 101 synchronous breast cancer cases and 115 metachronous breast cancer cases (interval to the second tumor &gt; 1 year). The items examined were age, tumor size, lymph nodal status, histological type, and biological markers (ER, PgR, HER2, p53 and Ki-67 index values) in the cases with paired data.
Results
1. The incidence of metachronous tumors was relatively stable at 2.1–2.7% throughout the period. On the other hand, the incidence of synchronous tumors has increased to 4.4% in the most recent 5-year period and the median interval was 7.1 years.
2. There was no difference in the tumor size of both tumors in the synchronous group, but the second tumor was significantly smaller than the first tumor in the metachronous group (2.2cm to 1.7cm). The node negative rates showed no difference between two groups.
3. The cases with DCIS were seen in 20% and 25% of the synchronous group and 12% and 16% of the metachronous group. Most of the patients (94.3%) with invasive cancer received systemic adjuvant therapy in the metachronous group.
4. The ER positive rates of both tumors were 87.1% and 88.1% in the synchronous group and 71.6% and 68.4% in the metachronous group, respectively. The concordance rates were higher in the synchronous group (p=0.02). Moreover, there was a significant difference in ER positive rates between the two groups (p=0.01) and the ER negative tumors were more frequent in the second tumor of the metachronous group. The PgR negative tumors increased in the second tumor of metachronous cases. The shorter the interval (&lt; 5years), the more the ER positive rate decreased (p=0.002). However, the longer interval did not correlate with the change of receptor status.
5. The Ki-67 index values significantly increased in the second tumor of the metachronous group, especially in the cases with a shorter interval. However, there was no difference in the synchronous group. The p53 overexpression rates significantly increased in the cases with a shorter interval.
6. The postoperative prognosis for the first tumor did not differ in both groups.
Conclusion
The incidence of synchronous bilateral breast cancer cases have increased but have remained relatively stable in the metachronous group. The concordance rates of the ER, PgR, Ki-67 and p53 status were higher in the synchronous group but the cases with negative ER, negative PgR, higher Ki-67 values and positive p53 increased in the second tumor of the metachronous group. These findings suggest that adjuvant systemic therapy played a important role in the treatment of bilateral breast cancer but the secondary tumor was more aggressive in the metachronous cases.
Citation Format: Arima N, Nishimura R, Osako T, Nishiyama Y, Fujisue M, Okumura Y, Murakami K, Toyozumi Y. The difference between metachronous and synchronous bilateral breast cancer in terms of clinical features and biology. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-09-26.