Pre-treatment imaging and pathology characteristics of invasive breast cancers of limited extent: potential relevance for MRI-guided localized therapy.

BACKGROUND AND PURPOSE: Identifying breast cancers of limited extent (BCLE) is becoming increasingly important, especially for (image guided) minimally invasive therapy and partial breast irradiation. The purpose of this study is to establish characteristics at functional imaging and pathology associated with invasive BCLE. MATERIALS AND METHODS: Seventy-five patients (77 breasts) with invasive breast cancer were prospectively included. Excision specimens were processed using complete embedding. Microscopic findings were reconstructed and correlated with contrast-enhanced MRI. Tumors were stratified by absence or presence of occult disease ≥10 mm from the MRI-visible lesion: BCLE and non-BCLE, respectively. Imaging and pathology characteristics were evaluated for their ability to discriminate between BCLE and non-BCLE. Multivariate binary logistic regression was employed to create a prediction model for BCLE. RESULTS: At univariate analysis, imaging as well as pathology characteristics were indicative for BCLE (39/77=51%). At multivariate analysis, a mass on mammography, the absence of tumor washout, positive ER and low quantity of DCIS in the index tumor retained significance (area under ROC curve=0.87). CONCLUSIONS: Pre-treatment assessment of mammography findings, MRI washout kinetics, ER status and quantity of DCIS in the index tumor has the potential to accurately identify BCLE.

Precise correlation between MRI and histopathology - exploring treatment margins for MRI-guided localized breast cancer therapy.

BACKGROUND: Magnetic resonance imaging (MRI) is more often considered to guide, evaluate or select patients for partial breast irradiation (PBI) or minimally invasive therapy. Safe treatment margins around the MRI-visible lesion (MRI-GTV) are needed to account for surrounding subclinical occult disease. PURPOSE: To precisely compare MRI findings with histopathology, and to obtain detailed knowledge about type, rate, quantity and distance of occult disease around the MRI-GTV. METHODS AND MATERIALS: Patients undergoing MRI and breast-conserving therapy were prospectively included. The wide local excision specimens were subjected to detailed microscopic examination. The size of the invasive (index) tumor was compared with the MRI-GTV. The gross tumor volume (GTV) was defined as the pre-treatment visible lesion. Subclinical tumor foci were reconstructed at various distances to the MRI-GTV. RESULTS: Sixty-two patients (64 breasts) were included. The mean size difference between MRI-GTV and the index tumor was 1.3mm. Subclinical disease occurred in 52% and 25% of the specimens at distances ≥10mm and ≥20mm, respectively, from the MRI-GTV. CONCLUSIONS: For MRI-guided minimally invasive therapy, typical treatment margins of 10mm around the MRI-GTV may include occult disease in 52% of patients. When surgery achieves a 10mm tumor-free margin around the MRI-GTV, radiotherapy to the tumor bed may require clinical target volume margins >10mm in up to one-fourth of the patients.