When a pathologist looks at a breast needle core biopsy, he or she looks over the entire prepared tissue biopsy to survey what is normal and what is abnormal. At low microscopic power, it is like flying over land to look at its various aspects, whether it is meadows, plowed fields, a city or town, or a mountain. This first view is to get an idea of what is normal and abnormal, and what the mammographer saw on mammogram originally to warrant doing the biopsy.
As the pathologist “flies over” the tissue on the slide, in this case, he sees abnormally enlarged ducts that are many times bigger than normal. This requires a closer look, and so the pathologist switches to a higher power lens and focuses on these enlarged ducts.
As you can see, here are clustered large ducts that are filled with many cells. This cellular proliferation or growth remains in the duct or tubule, causing it to expand and enlarge. These malignant cells are all abnormal, and there are no layers. Normal ducts are lined by two cell layers, and the outer cells are different from those in the inner layer. Please refer to the blog on normal breast in this Show Me series.
Now what about in situ? What does that mean? In situ means in place; the cancer cells are growing in place or inside the duct: non-invasive and in place. When the malignant cells are growing inside the duct, it is called Ductal Carcinoma In Situ—DCIS. (Once the cells start to grow outside the duct, they are invading adjacent tissue and are invasive.)
We should remember that malignant cells in general do not have a feed-back regulatory function to stop growth. Malignant cells grow and multiply and don’t stop this process. There is no self control or stopping mechanism. So with DCIS, malignant cells grow “out of control” inside the ducts. The malignant cells grow down the duct system toward the nipple. This is a non-invasive growth because these abnormal cells stay inside the duct, and because of inside-only growth, there is no invasion by definition.
What I am getting ready to tell you is hard to understand and hard to believe. Because the malignant cells stay inside the ducts, and often grow toward the nipple, the extent of the disease may be such that a larger excision is required than for an invasive tumor. The non-invasive disease can grow unchallenged down the duct toward the nipple; without resistance, DCIS can grow over considerable distances sometimes. Here is the hard part: because of its unrestrained growth toward the nipple, non-invasive DCIS may require a larger excision or mastectomy while an invasive tumor is often successfully treated with lumpectomy. It all has to do with extent of disease, and the non-invasive lesion can require more tissue to be removed (bigger surgery) than a purely invasive tumor.