What is invasive ductal carcinoma (IDC)?

Invasive ductal carcinoma (IDC), also known as infiltrating ductal carcinoma, is cancer that begins growing in the breast duct and then invades the fatty tissue of the breast outside of the duct. IDC is the most common form of breast cancer, representing 80 percent of all breast cancer diagnoses.

There are four types of invasive ductal carcinoma that are less common:

• Medullary Ductal Carcinoma - This rare type of cancer occurs in only three to five percent of cases. The tumor may feel more like a spongy change of breast tissue rather than a standard lump. This kind of tumor usually shows up on a mammogram.
• Mucinous Ductal Carcinoma - This type of cancer occurs when cancer cells within the breast produce mucous, which also contains breast cancer cells. The cells and mucous combine to form a tumor. Pure mucinous ductal carcinoma carries a better prognosis than more common types of IDCs.
• Papillary Ductal Carcinoma - This cancer looks like tiny fingers under the microscope. This cancer only becomes invasive in rare cases. It is common in women age 50 and older. Treatment for this kind of cancer is similar to the treatment for ductal carcinoma in situ, a less aggressive form of cancer.
• Tubular Ductal Carcinoma - This rare type of cancer occurs in only about two percent of cases. Tubular ductal carcinomas are small estrogen-receptor positive cancers, which means they respond to hormones. The cancer looks like hundreds of tiny tubes under the microscope. It is more common in women older than 50.