Previous research has demonstrated that chronic inflammation facilitates cancer progression and spread to other sites. The effect of acute inflammation in the microenvironment of the tumor that develops as a result of standard biopsy procedures has not been studied in detail. Recent studies demonstrated that acute inflammation in mouse models from a mammary biopsy increases the frequency of distal cancer metastasis. Core needle biopsies are the standard procedure for breast cancer diagnosis, but there have been no studies detailing the inflammatory response from the biopsy. The purpose of this study is to determine if core needle biopsies in breast cancer patients trigger an inflammatory response, determine the type of inflammatory response that occurs and study the potential effect of acute inflammatory response on tumor cells remaining. The biopsy wound site was identified in primary tumor resection samples from breast cancer patients. The inflammatory response adjacent and distant to the biopsy were studied via histology and immunohistochemistry. Tumor cell proliferation was studied as well. Our study demonstrated that diagnostic core needle biopsies trigger inflammatory cell recruitment at the site, and those cells remain over long periods of time. An unexpected increase in eosinophils were found to accumulate at the biopsy site. The biopsy also was shown to increase proliferation adjacent to the wound site. Overall, core needle biopsies used for breast cancer diagnosis induce a unique inflammatory environment at the site of the biopsy as well as the closely surrounding cells. Inflammation induced by the biopsy could lead to tumor cell progression or metastasis in breast cancer. These findings may be important for the clinical management of breast cancer. Citation Format: Spencer BL, Szalayova G, Ogodnik A, Rincon M, James T. Human breast cancer biopsies induce eosinophil recruitment and enhance adjacent cancer cell proliferation [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-03-09.