Breast cancer is the most common cancer in women, and about one in five breast cancer patients will hear their doctor say, “You have in situ breast cancer! Or, “You have stage zero breast cancer! What is stage zero and what is in situ cancer? Should we treat it? Let’s take a look. Let’s take a look at what cancer is. Cancer means cells that have mutated and lost control, keep dividing and replicating, and invade normal tissues. When we talk about carcinoma in situ, we usually refer to “ductal carcinoma in situ”, which is called ductalcarcinomainsitu, abbreviated as DCIS, which means that the cells in the duct have changed into cancer cells but have not yet passed through the wall of the duct and have not yet invaded the adjacent tissues. Because it has not yet expanded into nearby areas, it will not metastasize distally to other parts of the body. Since the cells are still in the same place, it is called “carcinoma in situ” and can also be described as stage 0 breast cancer. In stage 0 breast cancer, a few patients may notice abnormal discharge from the nipple or feel a lump in the area, but most people do not have symptoms. Then how do you know you have stage 0 breast cancer? Usually, it is because during the screening mammogram, abnormal calcifications are accidentally found, and the physician arranges for tissue sampling (biopsy), and the pathology report confirms that the cancer cells have not yet left the milk ducts and have not yet invaded the surrounding area, and then stage zero breast cancer is recognized. Basically, there is no way to tell from the breast ultrasound or mammography report that it is stage zero breast cancer. These two types of imaging examinations are to find the tumors or calcification points that are suspicious and to perform further biopsy on these suspicious tumors or calcification points. To determine stage zero breast cancer, both require pathological tissue slide reports. Then, since stage zero breast cancer means that there is no evidence of invasion of breast cancer cells into other tissues and organs. But with the passage of time, will the cancer cells that were originally staying in the same location come out of the woodwork and expand their sphere of influence, taking over our body and laying down one city after another? It is reasonable to suspect so. According to statistics, if in situ breast cancer is not treated, 20% to 50% of in situ cancers will progress to invasive cancers, and some physicians will use the phrase “about one-third” to tell patients that the chance of stage zero breast cancer progressing to invasive breast cancer is about one-third. As to whether this is a high or not high chance, it is a matter of opinion. However, physicians are not fortune-tellers, and there is no scientific way to predict whose stage zero breast cancer will progress to invasive breast cancer and whose stage zero breast cancer will remain in situ. At present, if a patient is diagnosed with stage zero breast cancer, most physicians still recommend that the patient receive treatment at the time of stage zero breast cancer because the prognosis is very good and the survival rate is nearly 100%. There is even a study that found that women who are over 50 years old and found to have stage zero breast cancer have a lower chance of dying in the next 10 years due to various reasons than the general public, probably because this is a group of people who can find stage zero breast cancer and are usually willing to undergo routine screening and pay more attention to their health. Treatment for breast cancer in situ is usually directed at the breast lesion. For surgery, you can choose breast conservation surgery or total unilateral mastectomy. If the extent of stage zero breast cancer is large, or if there are multiple (more than one) stage zero breast cancers, or if cancer cells are found at the edge of the body after breast-conserving surgery, total unilateral mastectomy should be considered. In addition, breast-conserving surgery is usually combined with radiation therapy to reduce the chance that the remaining breast cells will reappear as stage 0 or invasive breast cancer. Unless the extent of stage zero breast cancer is very small and the pathology reveals a very early stage, electrotherapy may not be considered. When breast surgery is performed, the surgeon will often perform an examination of the anterior lymph nodes to check for lymph node metastases. (For more information on the concept of sentinel lymph nodes, see “What should I do if I have stage I breast cancer?”) After the surgery, it is important to understand the characteristics of the test and then provide additional treatment according to the patient’s condition. If the test reveals that the patient has hormone ER and PR positive receivers, the patient may be asked to take hormone suppressants for five years to reduce the hormonal stimulation of the body and to reduce the chance of subsequent recurrence of carcinoma in situ or breast cancer in both the left and right breast. After being diagnosed with stage zero breast cancer, if you do not plan to undergo surgery immediately, it is important to discuss with your physician to determine the appropriate time for observation and follow-up so that stage zero breast cancer does not progress to invasive breast cancer without your knowledge. The stage 0 breast cancer we are discussing here is all in situ breast duct cancer. Another possible finding after tissue biopsy is lobularcarcinomainsitu (LCIS), or lobular carcinoma in situ. In the past, lobular carcinoma in situ was considered stage zero breast cancer, but now the American Cancer Society does not consider it to be stage zero cancer, and even if left untreated, this area usually does not progress to invasive breast cancer. However, these patients are seven to twelve times more likely than the general population to develop breast cancer in both breasts. Therefore, it is also important to work with your physician to regularly track the condition of your breasts and to evaluate and consider all possible ways to prevent the development of breast cancer.