Ductal dilatation of the breast is not cancerous, but it can occur at the same time as breast cancer. Most of the time, it occurs in women during their childbearing years. Some of the ducts in the breast may not be open, and after blockage, the distal ducts may not be drained, causing the distal ducts to dilate, and something may accumulate in this extensive dilatation. After the dilation, a large number of cells, such as lymphocytes and plasma cells, will try to carry away the material inside, so under the microscope you can see a large number of lymphocytes and plasma cells infiltrating the ducts, so it is also called plasmacytic mastitis, but plasmacytic mastitis is almost never cancerous.