Abstract P5-23-06: Metastatic pattern in stage IV male breast cancer at initial diagnosis: A population-based study
Authors: Leone JP , Leone BA , Zwenger AO , Vallejo CT , Romero AO , Machiavelli MR , Perez JE , Leone J 
Published: February 2018

Background: Male breast cancer (MaBC) is a relatively uncommon disease, representing less than 1% of all breast cancers. Although men tend to present at more advanced stages, the prognostic influence of metastatic pattern (MP), sites of metastases and factors associated with specific organ involvement are unknown. The primary aim of this study was to analyze the influence of MP compared with other biologic and clinical factors in the survival of patients (pts) with stage IV breast cancer at initial diagnosis (BCID). Secondary aims were to describe sites of metastases and evaluate factors associated with specific sites of metastatic spread.

Methods: We evaluated men with microscopically confirmed stage IV BCID with known metastatic sites, reported to the Surveillance, Epidemiology and End Results (SEER) 18 registries program from 2010 to 2014. Pts with other primary tumor either before or after breast cancer were excluded. MP was categorized as bone only, visceral (lung, liver or brain), bone and visceral and other. Pt characteristics were compared between MP. Univariate and multivariate analyses determined the effects of each variable on overall survival (OS). Logistic regression examined factors associated with specific sites of metastases.

Results: We included 136 pts. Median age was 63 years (range 28-91). At diagnosis, bone only metastases represented 31.6% of pts, visceral 16.2%, bone and visceral 38.2% and other 14%. Median OS for the entire cohort was 33 months (95% CI 19 months – not reached). Bone was the most common site of metastases (69.9%), followed by lung (44.9%), liver (14%) and brain (8.1%). OS rate at 3 years by MP was: bone only 46.05%, visceral 53.57%, bone and visceral 37.23% and other 70.56% (p=0.41). There were no significant differences in pt or tumor characteristics between MP. However, in adjusted logistic regression, triple negative (TN) and ER/PR+/HER2+ tumors had higher odds of brain metastases than ER/PR+/HER2- (all p&lt;0.05). Also, ER/PR+/HER2+ tumors had higher odds of liver metastases (p=0.027). Univariate analysis showed that older age (HR 1.7; p=0.03), no surgery (HR2.5; p=0.005), TN tumors (HR 5.6; p&lt;0.001) and pts with brain metastases (HR 4.2; p&lt;0.001) had worse prognosis. In multivariate analysis, TN subtype (HR 4.2; p=0.001) and pts with brain metastases (HR 3.44; p=0.012) had significantly shorter OS.

Conclusions: To our knowledge, this is the first study of MP in MaBC. The cohort had an acceptable median OS which did not differ significantly according to MP. Although brain metastases were less common, it is important to recognize their worse prognosis. Independent predictors of OS included tumor subtype and brain metastases. Tumor subtype had a clear influence on specific sites of metastases, particularly for brain and liver involvement.

Citation Format: Leone JP, Leone BA, Zwenger AO, Vallejo CT, Romero AO, Machiavelli MR, Perez JE, Leone J. Metastatic pattern in stage IV male breast cancer at initial diagnosis: A population-based study [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-23-06.