['We evaluated the effect of time to surgery on tumor growth by comparing initial imaging and pathologic tumor size estimates. We also determined predictors of delay to surgery.', 'Preoperative work-up, coordination of reconstructive surgery, and referral to tertiary care centers can delay surgical treatment of breast cancer. Whether these delays are associated with interim tumor progression is unknown.', 'We identified 818 clinically node-negative breast cancer patients at our cancer center who had undergone surgery as their first therapeutic modality for invasive breast cancer from September 2003 to December 2006. Baseline tumor size was determined by mammography and sonography; tumor size at surgery was determined from pathology reports.', 'The median time from imaging to surgery was 21 days (1-132 days). In multivariate analysis, increased time to surgery was associated with older age, total mastectomy versus breast-conserving surgery, and reconstructive surgery. The median difference from baseline mammographic tumor size to surgery was 0 cm (8.6 cm smaller to 7.3 cm larger at surgery). The median difference from baseline sonographic tumor size to surgery was 0.1 cm (7.5 cm smaller to 8.3 cm larger at surgery). Neither of these differences was significantly associated with time to surgery. Time to surgery was associated with positive lymph nodes at surgery; however, no association was found after controlling for other prognostic factors.'] Are delays in primary surgical treatment associated with significant tumor size progression in breast cancer patients?