Accurate determination of HER2/neu status in breast carcinoma is essential. Alteration of preanalytic variables is known to affect HER2/neu results. American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) issued guidelines to standardize fixation for increased HER2/neu accuracy. We studied the effects of changing preanalytic variables on HER2/neu immunohistochemical and fluorescence in situ hybridization (FISH) results in a known HER2/neu+ invasive carcinoma. The clinical specimen was processed according to ASCO/CAP guidelines, with remaining tumor stored fresh without any fixatives for 4 days at 4°C and cut into core biopsy-sized pieces. Each was fixed in 10% formalin, 15% formalin, Pen-Fix (Richard-Allan Scientific, Kalamazoo, MI), Bouin solution, Sakura molecular fixative (Sakura Tissue-Tek Xpress, Torrance, CA), or zinc formalin for 0 to 168 hours. Immunohistochemical studies and FISH were performed. Compared with the clinical specimen, the samples showed no tumor degradation or marked difference by immunohistochemical studies, except the 1-hour 10% formalin and Bouin samples, or FISH, except the Bouin-fixed samples. Our study demonstrates that HER2/neu results remain accurate beyond ASCO/CAP-recommended preanalytic variables, with the exception of Bouin solution for FISH analysis.