Ductal Carcinoma In-Situ, or DCIS, is considered a pre-invasive or noninvasive breast cancer. It is Stage 0 breast cancer, and carries an excellent prognosis. In certain cases, DCIS can progress into an invasive breast cancer that can spread to tissue outside of the breast. At this time there is no reliable way to know which cases of DCIS will progress and which ones will not. The length of time it takes for DCIS to progress to invasive cancer is also unknown and likely variable. Therefore it is common to remove DCIS when detected. DCIS can recur after excision and may come back as DCIS or invasive cancer. Cure rates for DCIS that has been excised are as high as 98%, but 2% of patients may die from DCIS.
Most cases of DCIS cannot be felt, and will be detected by mammography. DCIS typically shows up as suspicious calcifications on a mammogram. Associated symptoms like pain or skin changes are very rare with DCIS. Occasionally DCIS may cause nipple discharge from one duct.
The breast is composed of two basic units: lobules that make milk and ducts that transport the milk. It is the cells lining the duct that can go “bad” in DCIS. If these abnormal cells, which are uncontrollably growing, stay inside the duct, they are referred to as Ductal Carcinoma In-Situ (DCIS). They are ductal cells that have become malignant, but they have remained in their original place (in-situ) and are thus a noninvasive cancer. When the abnormal cells break through the walls of the duct and invade the breast stroma (the tissue surrounding the ducts), then the noninvasive cancer has transformed into an invasive cancer. Invasive cancer, like infiltrating ductal carcinoma, has the potential to spread throughout the body. DCIS does not have the potential to spread throughout the body, which is why cure rates for DCIS that is treated can be as high as 98%.
As with invasive breast cancer, DCIS comes in different varieties, some with less aggressive features and others with more aggressive features. Some cases of DCIS have estrogen receptors (estrogen receptor positive) which allow anti-estrogen drug therapy (also called hormone blocking therapy), like Tamoxifen. Other cases of DCIS do not have estrogen receptors (estrogen receptor negative) and do not respond to hormone blocking therapy.
Because we cannot predict which DCIS will become invasive cancer, we need to treat DCIS carefully and appropriately. A low grade DCIS that is less than 1 cm (about ½ inch) in size, is probably the kind DCIS that will never cause a problem. But DCIS that is high grade, does not have estrogen or progesterone receptors and/ or is larger than 1 cm, may have a chance to cause trouble and should be treated appropriately. One day we will be able to distinguish between low risk DCIS and high risk DCIS. But not today.
In summary, DCIS is a noninvasive, stage 0 breast cancer that is contained within the milk ducts of the breast. It can be successfully treated in almost all patients.