A LOOK AT THE FEMALE BREAST & CANCER

What is breast cancer?

Breast cancer is a malignant tumor that starts in the cells of the breast. A malignant tumor is a group of cancer cells that can grow into (invade) surrounding tissues or spread (metastasize) to distant areas of the body. The disease occurs almost entirely in women, but men can get it, too.

The normal breast

To understand breast cancer, it helps to have some basic knowledge about the normal structure of the breasts, What is the breast made up of?

The female breast consists of a core made up of milk glands (called lobules) and ducts. This core is surrounded by a layer of fat, which in turn is covered by the skin. Milk is produced in the milk glands or lobules and collects in small ducts called terminal ducts. These terminal ducts join together to form larger ducts, which eventually drain, via the nipples.

The female breast starts to grow from puberty and is fully developed when the woman is in her twenties. During a woman’s reproductive period (approximately 20 to 40 years old), the breast is under the influence of oestrogens and progesterone (female hormones) whose levels vary with the menstrual cycle. This influence can cause the breast to be tender, hard and lumpy especially pre-menstrually. When a woman enters her thirties, the breast undergoes regression in which the milk glands and ducts become smaller and are replaced by fibrous and fat tissue.

Breast profile: 
A Ducts
B Lobules
C Dilated section of duct to hold milk
D Nipple
E Fat
F Pectoralis major muscle 
G Chest wall/rib cage

Enlargement
A Normal duct cells
B Basement membrane
C Lumen (center of duct)

Most breast cancers begin in the cells that line the ducts (ductal cancers). Some begin in the cells that line the lobules (lobular cancers), while a small number start in other tissues.

The lymph (lymphatic) system of the breast

The lymph system is important to understand because it is one way breast cancers can spread. This system has several parts.
Lymph nodes are small, bean-shaped collections of immune system cells (cells that are important in fighting infections) that are connected by lymphatic vessels. Lymphatic vessels are like small veins, except that they carry a clear fluid called lymph (instead of blood) away from the breast. Lymph contains tissue fluid and waste products, as well as immune system cells. Breast cancer cells can enter lymphatic vessels and begin to grow in lymph nodes.
Most lymphatic vessels in the breast connect to lymph nodes under the arm (axillary nodes). Some lymphatic vessels connect to lymph nodes inside the chest (internal mammary nodes) and those either above or below the collarbone (supraclavicular or infraclavicular nodes). 

If the cancer cells have spread to lymph nodes, there is a higher chance that the cells could have also gotten into the bloodstream and spread (metastasized) to other sites in the body. The more lymph nodes that have breast cancer, the more likely it is that the cancer may be found in other organs as well. This is important to know because it could affect your treatment plan. Still, not all women with cancer cells in their lymph nodes develop metastases, and some women can have no cancer cells in their lymph nodes and later develop metastases.

Benign breast lumps

Most breast lumps are not cancerous (benign). Still, some may need to be sampled and viewed under a microscope to prove they are not cancer.

Fibrocystic changes

Most lumps turn out to be fibrocystic changes. The term fibrocystic refers to fibrosis and cysts. Fibrosis is the formation of scar-like (fibrous) tissue, and cysts are fluid-filled sacs. Fibrocystic changes can cause breast swelling and pain. This often happens just before a woman's menstrual period is about to begin. Her breasts may feel lumpy and, sometimes, she may notice a clear or slightly cloudy nipple discharge.
                                          
                                                                                                  Extract from the site breastcancer.org