Histological determinants for different types of local recurrence after breast-conserving therapy of invasive breast cancer. Dutch Study Group on local Recurrence after Breast Conservation (BORST)

The purpose of this study was to determine which histological factors are associated with an increased risk for local recurrence in the breast after breast-conserving therapy for early breast cancer (TNM stage I and II) and whether risk patterns vary according to menopausal status and type of local recurrence. Through complete follow-up of the patients of eight regional radiation oncology departments, two cancer institutes and one surgical clinic in The Netherlands, 360 patients were identified with local recurrence in the breast after having received breast-conserving therapy (local tumour excision, axillary dissection and irradiation of the whole breast and a boost to the tumour bed) during the 1980s. For each case, two controls with a follow-up of similar duration without local recurrence were randomly selected. Histological slides of the primary tumour were reviewed. Among premenopausal patients the risk of recurrence for those younger than 35 years was significantly higher than that for premenopausal patients of 45 years or older (relative risk (RR) 2.9; 95% confidence interval (95% CI) 1.3-6.6, P < 0.05). The risk of recurrence at or near the site of the primary tumour was most significantly increased for patients with high grade extensive intraductal component (EIC) adjacent to the primary tumour (RR 4.1; 95% CI 1.7-9.8, P < 0.01). Microscopic margin involvement was an important risk indicator for diffuse recurrence and recurrence in the skin of the breast, especially in the presence of vascular invasion (RR 25; 95% CI 4.0-150, P < 0.001). To prevent local recurrence at or near the site of the primary tumour, local excision with a 1-2 cm margin of healthy tissue and a 15 Gy boost seemed adequate local treatment for patients with well differentiated EIC. In contrast, a wider surgical margin, a higher boost dose or mastectomy should be considered for patients with poorly differentiated EIC. Microscopic margin involvement in the presence of vascular invasion significantly increases the risk of diffuse recurrence or recurrence in the skin.