Abstract P1-07-24: Increased risk of contralateral breast cancer after diagnosis of microscopically invasive breast cancer: SEER 1998-2012
Authors: Thomas A , Weigel RJ , Leone JP , Spanheimer PM , Schroeder MC 
Published: May 2016

Abstract
Node negative microscopically invasive breast cancer (BC) is frequently associated with ductal carcinoma in situ (DCIS) and considered to have a similar prognosis. We evaluated women with T1micN0M0 (T1mic), DCIS and Stage I BC and report clinical characteristics, risk for subsequent contralateral breast cancer (CBC) and overall survival (OS).
Methods:
The study cohort included women diagnosed 1998-2012 and reported to Surveillance, Epidemiology, and End Result (SEER) data with DCIS, T1mic, or Stage I BC (not including T1mic). Subsequent CBCs were identified in patients with known laterality without contralateral mastectomy. Kaplan Meier models were used to estimate survival and time to CBC. Log-rank tests assessed differences in survival across groups
Results:
During the study period, 9,785 women were diagnosed with T1mic. Clinical features and risk of CBC are shown in the Table 1. Women with DCIS and T1mic were younger than those with Stage I BC. T1mic was more likely to be hormone receptor (HR) negative. Women with T1mic underwent mastectomy significantly more often than women with DCIS or Stage 1 BC. T1mic occurred more frequently in non-white women. Women with T1mic were significantly more likely to develop subsequent CBC than women with Stage 1 BC with a trend for increased CBC compared to women presenting initially with DCIS. Of those who develop CBCs 5.9% (DCIS), 11.2% (T1mic), and 14.6% (Stage 1) developed within 1 year (YR) of diagnosis of the index cancer. At 10 YRS these numbers were 73.7%(DCIS), 82.7%(T1mic) and 83.2% (Stage 1) (DCIS vs T1mic, p&lt;0.001 T1mic vs Stage 1, P= 0.048). At 10 YRS OS for women with CBC after initial BC was 89.5%(DCIS), 86.6%(T1mic) and 84.3%(Stage1) (DCIS vs T1mic, p=0.077, T1mic vs Stage1 p=0.293), Table 2.
Table 1 DCIS, T1mic, Stage I BC: Clinical Features and Contralateral Breast Cancer DCIST1micStage 1 (excluding T1mic) %%%p ^p ^^N49,6829,785248,307 Median Age5858620.719&lt;0.001HR positive85.0%72.8%86.5%&lt;0.001&lt;0.001Grade Well-moderately differentiated56.3%61.1%76.6% Poorly-undifferentiated43.7%38.9%23.4%&lt;0.001&lt;0.001Mastectomy22.7%36.7%24.1%&lt;0.001&lt;0.001Race White79.7%77.3%84.2% Black10.8%11.0%7.9%&lt;0.001&lt;0.001Other9.4%11.6%7.9% CBC*4.1%4.3%3.4%0.317&lt;0.001CBC**57.9%72.9%77.0%&lt;0.0010.021* Portion of full sample, **Of those who had a subsequent BC (ipsilateral or contralateral),^ DCIS vs T1mic,^^ stage I vs T1mic
Table 2 OS by Initial Stage and with CBC 5 YR10 YRp* OSOS DCISall97.3%88.4% develop CBC97.8%89.5%0.037T1micall96.3%88.9% develop CBC95.0%86.6%0.036Stage1 (excluding T1mic)all95.9%85.0% develop CBC86.9%84.3%0.001*Comparing survival of the stage cohort (all) with women diagnosed with that stage who develop CBC
Conclusion:
Women with T1mic were at increased risk for subsequent CBC relative to women with Stage I BC. When subsequent CBC occurred it developed earlier in women with T1mic than those with DCIS. Time course for this second event and survival with CBC at 10 years matched more closely with women diagnosed with Stage 1 BC. These findings offer suggestions about the biology of T1mic and may have implications for counseling these women on risk reducing strategies.
Citation Format: Thomas A, Weigel RJ, Leone JP, Spanheimer PM, Schroeder MC. Increased risk of contralateral breast cancer after diagnosis of microscopically invasive breast cancer: SEER 1998-2012. [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 P1-07-24.