This is a medical question of type : information 
 What is (are) Breast Cancer ? 
 Key Points
                    - Breast cancer is a disease in which malignant (cancer) cells form in the tissues of the breast.    - Sometimes breast cancer occurs in women who are pregnant or have just given birth.     - Signs of breast cancer include a lump or change in the breast.    - It may be difficult to detect (find) breast cancer early in pregnant or nursing women.     - Breast exams should be part of prenatal and postnatal care.    - Tests that examine the breasts are used to detect (find) and diagnose breast cancer.    - If cancer is found, tests are done to study the cancer cells.    - Certain factors affect prognosis (chance of recovery) and treatment options.
                
                
                    Breast cancer is a disease in which malignant (cancer) cells form in the tissues of the breast.
                    The breast is made up of lobes and ducts. Each breast has 15 to 20 sections called lobes. Each lobe has many smaller sections called lobules. Lobules end in dozens of tiny bulbs that can make milk. The lobes, lobules, and bulbs are linked by thin tubes called ducts.      Each breast also has blood vessels and lymph vessels. The lymph vessels carry an almost colorless fluid called lymph. Lymph vessels carry lymph between lymph nodes. Lymph nodes are small bean-shaped structures that are found throughout the body. They filter substances in lymph and help fight infection and disease. Clusters of lymph nodes are found near the breast in the axilla (under the arm), above the collarbone, and in the chest.
                
                
                    It may be difficult to detect (find) breast cancer early in pregnant or nursing women.
                    The breasts usually get larger, tender, or lumpy in women who are pregnant, nursing, or have just given birth. This occurs because of normal hormone changes that take place during pregnancy. These changes can make small lumps difficult to detect. The breasts may also become denser. It is more difficult to detect breast cancer in women with dense breasts using mammography. Because these breast changes can delay diagnosis, breast cancer is often found at a later stage in these women.
                
		        
		            Other Information About Pregnancy and Breast Cancer
		            
		                
		                    Key Points
		                    - Lactation (breast milk production) and breast-feeding should be stopped if surgery or chemotherapy is planned.     - Breast cancer does not appear to harm the unborn baby.    - Pregnancy does not seem to affect the survival of women who have had breast cancer in the past.
		                
		                
		                    Lactation (breast milk production) and breast-feeding should be stopped if surgery or chemotherapy is planned.
		                    If surgery is planned, breast-feeding should be stopped to reduce blood flow in the breasts and make them smaller. Breast-feeding should also be stopped if chemotherapy is planned. Many anticancer drugs, especially cyclophosphamide and methotrexate, may occur in high levels in breast milk and may harm the nursing baby. Women receiving chemotherapy should not breast-feed. Stopping lactation does not improve the mother's prognosis.
		                
		                
		                    Breast cancer does not appear to harm the unborn baby.
		                    Breast cancer cells do not seem to pass from the mother to the unborn baby.
		                
		                
		                    Pregnancy does not seem to affect the survival of women who have had breast cancer in the past.
		                    For women who have had breast cancer, pregnancy does not seem to affect their survival. However, some doctors recommend that a woman wait 2 years after treatment for breast cancer before trying to have a baby, so that any early return of the cancer would be detected. This may affect a womans decision to become pregnant. The unborn baby does not seem to be affected if the mother has had breast cancer.