PRIDE Foundation Malaysia What is Breast Cancer?

What is Breast Cancer?

A cancer is a group of cells that have grown in an uncontrollable way, damaging healthy tissues. A group of growing cancer cells forms a lump, which is called a tumour. If the tumour is in the breast, it is called breast cancer. Breast cancer is a malignant growth that begins in the tissues of the breast.


Whether your cancer is non-invasive or invasive will determine your treatment choices and how you might respond to the treatments you receive. The main types of breast cancer:

Non-invasive cancer

  • Ductal Carcinoma In Situ (DCIS)
  • Lobular Carcinoma In Situ (LCIS)

Invasive cancer

  • Invasive Ductal Carcinoma (IDC)
  • Invasive Lobular Carcinoma (ILC)

Non-invasive cancer (Carcinoma in situ)

When abnormal cells grow inside the lobules or milk ducts but have not spread to the surrounding tissue or beyond, the condition is called carcinoma in situ. The term “in situ” means “in place” and is used to describe this condition because the abnormal cells are still “in place” inside the lobules or ducts where they first developed. There are two main categories of carcinoma in situ: ductal carcinoma in situ and lobular carcinoma in situ.

Ductal Carcinoma In Situ (DCIS)
Mainly originates in the milk ducts of the breast. It is the most common form of non-invasive breast cancer (90%).

Lobular Carcinoma In Situ (LCIS)
Mainly originates in the lobules of the breast. It is less common and considered a marker for increased breast cancer risk.

The cells involved in the different carcinomas in situ are not fully cancerous because they have not developed the ability to invade out of the ducts or lobules and metastasize. They are often referred to as pre-cancerous conditions because they can either develop into or raise the risk of invasive cancer.

Invasive cancer

Invasive breast cancer is not the same as metastasis.

Metastasis occurs when the cancer cells break away from the primary tumour and spread into organs in other parts of the body through the bloodstream or the lymphathic system. Most invasive cancers are either ductal or lobular in nature. If the cancer cells spread outside the ducts or lobules of the breast into the surrounding tissue, this is called invasive breast cancer.

Invasive cancer cells sometimes spread outside the breast area to other parts of the body. They do this by moving through blood vessels, such as veins, or through lymphatic vessels. Lymphatic vessels are next to veins in the body, and are connected to lymph nodes (glands). Lymph nodes collect normal fluid and dead cells from the lymphatic vessels.

Invasive Ductal Carcinoma (IDC)
Accounts for about 80% of all breast cancers. Invasive means that it has “invaded” or spread to the surrounding tissues. It is ductal because the cancer began in the milk ducts—which are the “pipes” that bring milk from the lobules to the nipple.

Invasive Lobular Carcinoma (ILC)
Accounts for about 10%–15% of all breast cancers, in which the cancer has spread from the lobules to the surrounding tissues. It is often found in multiple sites in the breast and can be difficult to detect by physical examination or mammography.


Medullary Carcinoma
It is a rare cancer of ductal origin, accounting for 5% of breast cancers. Distinctive features include large size at detection, soft texture on palpation, mobility due to lack of invasion and the presence of immune system cells at the edges of the tumor. The outlook, or prognosis, for this kind of breast cancer is better than for other types of invasive breast cancer. But these are often hard to distinguish from infiltrating ductal carcinoma and are treated the same way.

Paget’s Disease of the Nipple
It is rare, slow-growing cancer producing changes in the nipple and accounts for only 1% of all cases of breast cancer. This type of breast cancer starts in the breast ducts and spreads to the skin of the nipple and then to the areola, the dark circle around the nipple. The skin of the nipple and areola often appears crusted, scaly, and red, with areas of bleeding or oozing. The woman may notice burning or itching. Paget disease may be associated with in situ carcinoma or with infiltrating breast carcinoma. If no lump can be felt in the breast tissue and the biopsy shows DCIS but no invasive cancer, the prognosis is excellent.

Mucinous Carcinoma
This rare type of invasive breast cancer is formed by mucus-producing cancer cells. The prognosis for mucinous carcinoma is better than for the more common types of invasive breast cancer. Colloid carcinoma is another name for this type of breast cancer.

Inflammatory carcinoma
This uncommon type of invasive breast cancer accounts for about 1% to 3% of all breast cancers. It makes the skin of the breast looks red and feels warm and gives the skin a thick, pitted appearance, mimicking an inflammation with no evidence of a lump. Doctors now know that these changes are not caused by inflammation or infection, but by cancer cells blocking lymph vessels or channels in the skin.

Phyllodes tumor
This very rare breast tumor develops in the stroma (connective tissue) of the breast, in contrast to carcinomas, which develop in the ducts or lobules. Phyllodes (also spelled phylloides) tumors are usually benign but on rare occasions may be malignant.

Benign phyllodes tumors are treated by removing the mass and a narrow margin of normal breast tissue. A malignant phyllodes tumor is treated by removing it along with a wider margin of normal tissue, or by mastectomy. These cancers do not respond to the usual treatments for invasive ductal or lobular breast cancer. In the past, both benign and malignant phyllodes tumors were referred to as cystosarcoma phyllodes.

Tubular carcinoma
Is another special type of infiltrating breast carcinoma, in which the cells looks like a tubular under the microscope. Tubular carcinomas account for about 2% of all breast cancers and have a better prognosis than infiltrating ductal or lobular carcinomas.