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Introduction: Breast cancer remains the most common cancer in women. Although treatment advances have improved the prognosis for many women, many existing therapies have significant associated toxicities. A major goal of current research is to develop targeted therapies based on characteristics of each individual's cancer. Polyploidy can provide a potential difference between cancer and normal cells that can be harnessed to selectively destroy cancer cells. We hypothesize that polyploidy is common in aggressive triple negative breast cancer. If this is the case, polyploidy could provide a target for therapy in triple negative cancers. Methods:We conducted a retrospective review of data collected by the University of Wisconsin Tumor Registry and HER2 testing by the state lab of hygiene between 2003 and 2011. Patients from the two data sets were matched by name and/or medical record number. Tumors were considered polyploid if ≥3 CEP17 signals were detected. Chi square testing and student T-tests were used to identify statistical correlations. Results: A total of 1211 were identified meeting eligibility criteria and 170 women had polyploid tumors. Of these, 72 had unknown or equivocal results for ER/PR or HER2 and were excluded from analyses. Polyploid tumors correlated with TNBC (p=0.028) and hormone receptor negative cancer (p=0.02). Subgroup analysis showed a positive correlation between HER2 positive tumors and polyploid tumors (p=0.0005). Polyploidy tumors were more likely to be either stage I or stage IV (p=0.0019). Vital status at last contact and age at diagnosis were not significantly different between the two groups (p=0.2875 and 0.7826, respectively). Discussion:We conclude that polyploid tumors cross all known subtypes of breast cancer, but are enriched among triple negative cancers. This may represent a viable group of cancers that can be targeted with specialized therapy. Table 1 Polyploid Euploid P HER2- 122 857 0.0005 Hormone- 38 164 0.02 Triple negative cancers 29 121 0.028 Stage I 80 612 0.002 Stage II 54 275 Stage III 29 99 Stage IV 4 49 Unknown stage 3 6 Mortality 33 168 0.29 Mean Age 59 58 0.78 Citation Format: Amy Fothergill, Mark Burkard. Polyploidy across breast cancer subtypes. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1927. doi:10.1158/1538-7445.AM2013-1927