Background: Intraductal tumor extension is a characteristic feature of primary breast carcinoma, and is an important consideration in patients undergoing breast conservative surgery. However, there have been no reports of studies of intraductal extension within the mammary ductal tree.
Methods: Quadrantectomy specimens from 20 patients with primary invasive breast carcinoma were examined by subgross and stereomicroscopic technique to visualize intraductal tumor extension. Serial 2 mm-thick sections were subjected to two-dimensional (2-D) tumor mapping, measuring the distances and angles of extension, and to three-dimensional (3-D) reconstruction of the mammary duct-lobular systems by means of computer graphics.
Results: Intraductal tumor extension was found in 16 of 20 specimens (80.0%), extending continuously from the primary invasive carcinoma through the mammary ductal tree. The distances and angles of extension were larger in tumors with microcalcifications, papillotubular invasive ductal carcinoma, 30% or more of intraductal component, and comedo-type intraductal tumor extension. The 3-D reconstructions demonstrated three types of extension; central (11 cases), peripheral (3 cases), and mixed (2 cases). Further, there were some ductal branches anastomosing with different mammary duct-lobular systems at various sites. In one specimen, intraductal tumor extended widely from the primary invasive carcinoma through a branch connecting adjacent mammary duct-lobular systems.
Conclusions: Three-dimensional reconstruction images of intraductal extension of invasive breast carcinomas are presented for the first time to the authors' knowledge. Examples of ductal anastomoses were observed, and should be considered as a risk factor for possible widespread intraductal extension through multiple mammary duct-lobular systems.