Ductal Carcinoma:
An invasive (infiltrating) carcinoma of the breast. This carcinoma in which no special histological feature is recognized is designated NOS or Not Otherwise Specified and is by far the most common ductal tumor, accounting for almost 70% of breast cancers. It is characterized by stony hardness upon palpation. It commonly metastasizes to the axillary lymph nodes and its prognosis is the poorest of the various ductal types. (DeVita Jr et al., Cancer: Principles & Practice of Oncology, 3d ed, p1205)
