DCIS- Ductal carcinoma in situ is the proliferation of

### Malignant epithelial cells within the confines of mammary ducts and lobule without invasion through the basement membrane

## Step1: Understanding DCIS### DCIS stands for Ductal Carcinoma in Situ. It is a type of non-invasive breast cancer that originates in the milk ducts of the breast.## Step2: Identifying the Cellular Nature### DCIS involves the proliferation of malignant epithelial cells. These cells are cancerous and originate from the epithelial lining of the ducts.## Step3: Location of the Cells### The malignant epithelial cells are confined to the mammary ducts and lobule. They do not spread beyond these structures.## Step4: Invasion Status### DCIS is characterized by the lack of invasion through the basement membrane. This means the cancer cells do not break through the basement membrane of the ducts into surrounding tissues.