Question: What is the difference between in situ and invasive breast cancers?
Answer: Invasive breast cancer is the classic type of cancer that we've been dealing with for several thousand years, really. It is the type of malignant cell that can spread to other places in the body where, what is called metastasized, and thereby do further damage to the patient.
In situ cancers are recognizable as malignant cells themselves, but they haven't yet begun to act in a malignant fashion. It's a difficult concept to understand. But the cells do not spread; they do not go past the breast. So if we could, for example, pick up all cancers when they are in situ instead of invasive, we could probably be curing almost all of the patients who have this or these diseases.