Medullary carcinoma of the breast is a rare subtype of invasive ductal carcinoma (cancer that begins in the milk duct and spreads beyond it), accounting for about 3-5% of all cases of breast cancer. It is called “medullary” carcinoma because a tumour is a soft, fleshy mass that resembles a part of the brain called the medulla.
Medullary carcinoma is more common in women who have a BRCA1 mutation. Studies have shown that medullary carcinoma is also more common in Japan than in the United States.
Medullary carcinoma cells are usually high-grade in their appearance and low-grade in their behaviour. In other words, they look like aggressive, highly abnormal cancer cells, but they don’t act like them. Medullary carcinoma doesn’t grow quickly and usually doesn’t spread outside the breast to the lymph nodes. For this reason, it’s typically easier to treat than other types of breast cancer.