Breast cancer is a disease in which malignant (cancerous) cells form in the breast tissues. 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. The lobules end with dozens of small glands that produce milk. The lobes, lobules, and glands are connected by thin tubes called ductules. Each breast also has blood and lymph vessels. Lymph vessels carry lymph between lymph nodes. Lymph nodes are located throughout the body. They filter lymph and store white blood cells that help fight infection. Clusters of lymph nodes are found near the breast in the axilla (under the arm), above the collarbone, and in the breast itself. In some cases, breast cancer occurs in women who are pregnant or have just given birth. Breast cancer occurs approximately once in every 3,000 pregnancies. It occurs most often in women between the ages of 32 and 38. As the average age at first birth for women increases, the number of new cases of breast cancer is likely to increase. Diagnosing breast cancer in pregnant and lactating women can be difficult in the early stages of the disease. During pregnancy or after giving birth, the breasts usually become larger, firmer and denser. This happens due to the normal hormonal changes that occur during pregnancy. These changes can make it difficult to detect small lumps and therefore the diagnosis of the disease is made at a later stage. Breast exams should become part of prenatal and postnatal care. The following tests and procedures may be used: Physical examination; Ultrasound of the mammary gland; Mammography – the risk to the fetus is minimal. But mammograms in pregnant women may appear negative despite the presence of malignancy; Biopsy If a tumor is detected, it is necessary to carry out a number of tests. The decision about the best treatment is based on the results of these tests and the gestational age of the fetus. The tests give information about how fast the tumor is growing, how likely it is to spread to other parts of the body, and how likely it is to achieve the desired effect of the treatment. These may include: Test for estrogen and progesterone receptors. This test measures the amount of estrogen and progesterone receptors in the malignant tissue. If there are more estrogen or progesterone receptors than normal, the cancer is called receptor-positive. This type of breast cancer can grow faster. Human epidermal growth factor type 2 (HER2) test. This type of breast cancer can grow faster and spread to other parts of the body. It can be treated with drugs that target the HER2 protein after birth. A given malignancy can be described as triple negative or triple positive. In the case of a triple negative formation it means,that the cells of the tumor under study lack estrogen and progesterone receptors or a higher than normal amount of HER2 receptors. If estrogen, progesterone receptors and a higher than normal amount of HER2 receptors are found in the examined tumor, it is a triple positive tumor. This information is important to give the best treatment. There are drugs that can stop the binding of receptors to estrogen or progesterone and stop the development of the tumor. Other drugs can be used to block HER2 receptors on the surface of breast cancer cells and stop them from growing.