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Introduction: Growing evidence demonstrates activity of neoadjuvant carboplatin in triple negative breast cancer (TNBC). Underlying germline and somatic Homologous Recombination (HR) repair deficiency may predict response to DNA damaging agents like platinum compounds in TNBC. Certain DNA repair machinery genes (Fanconi Anemia gene) are also involved in the maintenance of hematopoetic stem cell (HSC) function and impaired repair of DNA double strand breaks can lead to HSC and progenitor cell dysfunction. Thus, in presence of HR defects DNA damaging chemotherapy may lead to unique hematological toxicity. It is also possible that in presence of HR defects breast cancer response and hematological toxicity with DNA damaging agents will parallel each other. Aim: To evaluate the impact of hematological toxicity on response to neoadjuvant Carboplatin/Docetaxel chemotherapy in patients with sporadic and BRCA associated TNBC utilizing clinical and BRCA mutation data from a prospective TNBC registry. Methods: 288 patients with Stage I (T>1cm) II and III TNBC were enrolled on a multisite prospective registry between 3/2011 to 4/2014, out of which 49 patients received neoadjuvant Carboplatin AUC 6 + Docetaxel 75mg/m2 every 21 days (4-6 cycles) and have undergone breast surgery. Carboplatin was dosed using the modified Cockcroft-Gault formula. Hematologic toxicity was graded using the CTCAE version 4.03. All patients received prophylactic pegfilgrastim on day 2. Pathological complete response (pCR) was defined as absence of invasive disease in the breast and axilla. All patients underwent comprehensive BRACAnalysis®(Myriad). Results: For the 49 eligible patients median age was 50 years, median weight was 172 lbs, 18% were African American, and 37% had LN+ disease. 26% (13 /49) of patients carried deleterious BRCA mutation (9 BRCA1, 4 BRCA2). pCR of the cohort was 65%. Overall 61%, 96%, and 12 % patients demonstrated > Grade1 thrombocytopenia (Tp), anemia, or neutropenia, respectively; 4%, 6%, and 6% patients demonstrated grade 3/4 thrombocytopenia, anemia, or neutropenia, respectively. There was no association between pCR and anemia or neutropenia. Carboplatin dose reductions/delays/omission was more common in patients with Tp compared to patients without Tp (33% vs. 5%; p=0.02). Patients with Tp were more likely to achieve a pCR compared to patients without Tp (85% vs. 47%; p=0.013). 77% of BRCA carriers and 64% of BRCA wild type TNBC demonstrated Tp (NS). pCR rates in BRCA wild type patients with and without Tp were 82% and 47%, respectively (p=0.041). pCR rates in BRCA mutation carriers with and without Tp were 89% and 50%, respectively (p=0.20). On multivariable platelet count was independently associated with pCR (p=0.001)Conclusions: Tp was associated with decreased dose delivery of carboplatin but an improved pCR in BRCA wild type TNBC. Comprehensive assessment of HR defects beyond germline BRCA mutation status may be required to elucidate the biological process that explains this observation. Tp may be a harbinger of underlying HR deficiency and further correlative studies exploring this association of Tp with pathological response to carboplatin in TNBC are warranted. Citation Format: Priyanka Sharma, Benjamin C Powers, Bruce F Kimler, Claire Ward, Jennifer R Klemp, Carol S Connor, Marilee K McGinness, Joshua MV Mammen, Jamie L Wagner, Qamar J Khan, Roy A Jensen, Andrew K Godwin, Carol J Fabian. Thrombocytopenia is associated with pathological complete response to neoadjuvant carboplatin/docetaxel chemotherapy in BRCA wild type triple negative breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-06-16.