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Factors Associated with Negative Margins of Lumpectomy Specimen: Potential Use in Selecting Patients for Intraoperative Radiotherapy

¹ Department of Surgical Oncology, Princess Margaret Hospital, Toronto, Ontario, Canada
² Department of Biostatistics, Princess Margaret Hospital, Toronto, Ontario, Canada
³ Department of Radiation Oncology, Princess Margaret Hospital, Toronto, Ontario, Canada
⁴ Department of Pathology, Princess Margaret Hospital, Toronto, Ontario, Canada

Correspondence: Address correspondence and reprint requests to: D. R. McCready, MD, MSc, FRCSC; E-mail: david.mccready{at}uhn.on.ca

Background: Lumpectomy followed by radiation is standard treatment for early breast cancer. Recently, the use of partial breast intraoperative radiation (IORT) has been developed, and patients selected for IORT should not have positive margins. This study’s purpose was to identify factors predicting negative margins after lumpectomy.

Methods: Patient age, preoperative investigations, surgery, final pathology, and margin status were examined using a prospective database between 1999 and 2005. Univariate and multivariate logistic regression analysis were performed to identify patient and tumor factors predicting an increased rate of negative margins. The results were used to generate a patient selection algorithm.

Results: The rate of positive margins at first resection was 17% in 730 lumpectomies (708 patients). Multivariate analysis revealed that older age (P = .0006), smaller tumor size (P < .0025), type of surgery (OR = 3.4 for ultrasound vs mammogram-guided wire localization, P = .003), and having a core needle biopsy (CNB) with preoperative cancer diagnosis (P < .0001) were predictive for having a negative margin. Patients older than age 50 with a preoperative CNB showing invasive cancer less that 3 cm that can be localized under ultrasound had a negative margin rate of 98 % (n = 178). These patients would be ideal for consideration of IORT.

Conclusions: Negative margin rates after lumpectomy are predicted by age, tumor size, preoperative investigations, and localization technique. These variables can be used to select patients for IORT with a 2.2% chance of positive margins.

Key Words: Breast cancer • Lumpectomy • Margin • Intraoperative radiotherapy