Magnetic resonance imaging estimation of breast cancer size after large core needle biopsy

Objective: To determine if the time interval between percutaneous core biopsy and subsequent breast MR imaging influences the accuracy of cancer size estimation. Methods: Patient records between January 2002 and January 2003 were reviewed to identify all patients who underwent breast MR imaging at our institution after percutaneous core biopsy of an invasive cancer, and who subsequently had lumpectomy or mastectomy with negative histologic margins. The maximum diameter of each lesion was prospectively measured by MR imaging and compared with pathologic measurement. MR imaging assessment of cancer size was scored as follows: true positive (10 mm or less discrepancy), false positive (MR imaging overestimates pathologic size by greater than 10 mm), and false negative (MR imaging underestimates pathologic size by greater than 10 mm). Patients were separated into two groups based on the time interval between percutaneous core biopsy and the subsequent MR imaging study (Group A, less than or equal to 14 days; Group B, greater than 14 days). The accuracy of MR imaging determination of cancer size was compared between the two groups. Results: Among the 114 patients who underwent breast MR imaging, 23 patients with 31 malignant lesions met the inclusion criteria. In Group A, there were 16 true positive and 1 false positive MR imaging assessments (94% accuracy). in Group B, there were 13 true positive and 1 false positive MR imaging assessments (93% accuracy). Conclusions: Magnetic resonance imaging performs equally well in determining the size of breast cancers within two weeks or more than two weeks after percutaneous core biopsy, in the absence of measurable hematomas. A delay between core biopsy and subsequent MR imaging is not warranted.