Introduction Breast Cancer

The human body is composed of millions of cells. These cells grow, multiply, eventually die, and get replaced. This is part of the normal life cycle of human cells. Cancer cells are abnormal, independent, and erratic. When cancer develops, these cells multiply without control and eventually form malignant tumors. These tumors have the potential to invade surrounding structures and spread to other parts of the body.

Most Breast Cancers Develop From the Milk Ducts:Breast cancer originates from different types of cells in the breast. The breast is composed of a ductal system (milk ducts), lobules (milk sacs), fat, and connective tissue (tissue that supports the breast). Most breast cancers originate from the milk ducts (invasive ductal carcinoma, ductal carcinoma in situ) or from the milk lobules (invasive lobular carcinoma).
Breast Cancer Cells Can Spread: refers to fluid that is present in the breast and comes out upon mechanical stimulation of the nipple and underlying ducts.

Breast cancer cells can spread to other parts of the body through the lymphatic and circulatory system. This is known as metastasis. The most common sites of metastasis includes the axillary lymph nodes, bone, lungs, liver and brain.

How Breast Cancer Develops? Breast cancer develops as consequence of changes in a gene or a group of genes. Each cell of the human body has thousands of genes inherited from our parents. Each gene is made up of a different sequence of DNA and each gene has a different function. The DNA directs the functioning of the cells. There are different types of genes. Some are called tumor suppressor genes. Their function is to prevent the formation of cancer cells. We can visualize them as the police force. Their role is to keep the cells in order and repair the DNA when it is damaged. A mutation or abnormality in one of these genes may impair their function, and as a result cells will continue to grow and can eventually form a malignant tumor. Examples of tumor suppressor genes are BRCA1, BRCA2, p53, and PTEN, to name a few. A mutation in these genes can lead to a breast cancer. Oncogenes are another type of gene that can turn a normal cell into a cancerous one. There are other genes that can cause breast cancer, but have not been identified yet.

Gene Mutation: Acquired or Inherited: A gene mutation can either be acquired or inherited from our parents. Only 5% to 10% of breast cancers are inherited. Most of the inherited breast cancers are due to a mutation in the BRCA1 and BRCA2 tumor suppressor genes. Patients with hereditary breast cancer are predisposed to the disease because they are born with a genetic mutation. This mutation is passed from parent to child.
The vast majority of breast cancers are caused by mutations that are acquired throughout life. Acquired mutations are not passed from generation to generation. Some mutations have no effect on a cell, while others may lead to cancer. These mutations could be due to errors committed by normal human cells without an inciting cause or external factor. There are risk factors associated with different cancers. The gene mutations that can lead to breast cancer could be due to environmental factors, diet habits, a sedentary lifestyle, alcohol consumption, and hormones, just to name a few. Cancers due to mutations from external factors are called sporadic cancers. Unfortunately, we cannot specifically pinpoint which factor or factors trigger the cascade that leads to a cancer or what may actually cause the cancer.
Having a risk factor does not necessarily mean that a woman will get breast cancer. As a matter of fact, approximately 75% of women who develop breast cancer do not have any identifiable risk factors. A risk factor means a higher chance of getting the disease. We will discuss the different risk factors associated with breast cancer in the next section.