Ductal carcinoma starts in gland cells in the breast ducts. It is the most common type of breast cancer. It may be non-invasive (called ductal carcinoma in situ) or invasive.
Ductal carcinoma in situ (DCIS)
DCIS may also be called intraductal carcinoma or non-invasive ductal carcinoma. It is the most common type of non-invasive breast cancer. The cancer cells are only in the lining of the breast duct. They have not spread outside the duct into nearby breast tissue or to other organs in the body.
DCIS is usually too small to be felt in the breast, so it is most often found during a screening mammography.
DCIS is given a grade, which describes how DCIS cells look and how quickly they grow compared to normal cells. The 3 grades of DCIS are low, intermediate and high. Knowing the grade is important as it can help doctors predict how likely DCIS will come back after treatment or turn into an invasive breast cancer.
DCIS may also be described by how the cells look like under the microscope.
Comedo DCIS has cells that look like they have plugs of dead tissue in the centre. This type of DCIS is high grade, which means the cells are growing quickly, and it is more likely to come back after treatment. This type of DCIS is also more likely to become an invasive breast cancer.
Non-comedo DCIS is low grade or intermediate grade, which means that it is slow growing and less likely to become an invasive breast cancer.
Invasive ductal carcinoma
Invasive ductal carcinoma is also called infiltrating ductal carcinoma or ductal adenocarcinoma. It is the most common type of invasive breast cancer.
Invasive ductal carcinoma starts in the breast ducts, grows through the duct wall and grows into nearby breast tissue. The cells can continue to grow and cause a lump or thickening in the breast. The breast cancer cells can also spread (metastasize) to the lymph nodes and other parts of the body.
Doctors may classify invasive ductal carcinoma based on what the cancer cells look like under a microscope:
- invasive not otherwise specified (NOS), or no special type (NST)
- invasive with predominant intraductal component
- mucinous, or colloid
All of these different types of invasive ductal carcinoma are treated in the same way. The mucinous, papillary and medullary types are generally slow-growing and do not usually spread to the lymph nodes. Tubular invasive ductal carcinoma is less likely to come back after treatment. Scirrhous invasive ductal carcinoma grows faster than the other types.