According to the American Cancer Society, there are many types of breast cancer — and each type can be described in a number of ways by health care personnel. It’s easy for patients to become confused by details when they receive a breast cancer diagnosis.

It's important to understand that the breast cancer type is determined by the specific cells in the breast that are affected. The majority of breast cancers are carcinomas: a cancer arising in the epithelial tissue of the skin or of the lining of the internal organs. Carcinomas that form in the breast are often adenocarcinoma, a type of cancer that starts in the glands that line the inside of one of your organs. In breast cancer, the adenocarcinoma can start in cells in the milk ducts or the lobules (milk-producing glands).

The type of breast cancer can also refer to whether the cancer has spread or not:

• In situ breast cancer, such as ductal carcinoma in situ, starts in a milk duct but has not grown into the neighboring breast tissue.

• Invasive or infiltrating breast cancer describes any form of breast cancer that has invaded nearby breast tissue.

Following is a summary of four types of breast cancer:

1. Ductal carcinoma in situ

The National Cancer Institute defines ductal carcinoma in situ, or DCIS, as a noninvasive condition in which abnormal cells are found in the lining of a breast duct. The abnormal cells have not spread outside the duct to other tissues in the breast. In some cases, DCIS may become invasive, spreading to other tissue.

2. Invasive ductal carcinoma

Invasive ductal carcinoma, or IDC, is the most common type of breast cancer, according to the National Breast Cancer Foundation. IDC accounts for 70-80% of all breast cancer diagnoses. The cancer cells that first formed in the milk ducts gradually spread into other areas of the breast tissue.

3. Inflammatory breast cancer

According to the American Cancer Society, inflammatory breast cancer, or IBC, is a less-common type of invasive breast cancer. IBC can develop rapidly, making the affected breast red, swollen and tender. This form of breast cancer occurs when cancer cells block the lymphatic vessels in skin covering the breast. Because of this, it viewed as a locally advanced cancer — at least a stage III breast cancer. If it has spread to other parts of the body, it is considered stage IV.

4. Metastatic breast cancer

Also classified as stage IV cancer, metastatic breast cancer has spread to other parts of the body, which may include the lungs, liver, bones or brain. According to the American Cancer Society, most women with metastatic breast cancer are treated mainly with systemic therapy, which may include hormone therapy, chemotherapy or targeted therapy, either alone or in combination. In addition, local treatments such as surgery or radiation may be employed to help prevent or treat symptoms.

In addition to these forms of breast cancer, the National Breast Cancer Foundation provides information about several other types that are less commonly seen, including:

• Triple-negative breast — A cancer that tests negative for estrogen receptors, progesterone receptors, and excess HER2 protein.

• Medullary carcinoma — A rare subtype of invasive ductal carcinoma. It accounts for 3-5% of all breast cancer cases. It is called “medullary” carcinoma because the tumor is a soft, fleshy mass that resembles a part of the brain called the medulla.

• Tubular carcinoma — These cancer cells have a distinguishing tubular structure. Usually found through a mammogram, it is cluster of cells that can feel like a spongy area of breast tissue rather than a lump. This form of breast cancer usually occurs in women aged 50 and older. It accounts for about 2% of all breast cancer diagnoses.

• Mucinous carcinoma — Making up 1-2% of all breast cancer cases, mucinous carcinoma differs from other forms in its mucus production and cells that are poorly defined. It has a favorable prognosis in most cases.

• Paget disease of the breast — This condition is a rare type of cancer affecting the skin of the nipple and often the areola. According to the National Breast Cancer Foundation, most people with Paget disease evident on the nipple also have one or more tumors inside the same breast.

For more information on the various types of breast cancer, visit one of the following websites:

• National Cancer Institute at the National Institutes of Health – www.cancer.gov

• American Cancer Society – www.cancer.org

• National Breast Cancer Foundation – www.nationalbreastcancer.org

Breastcancer.orgwww.breastcancer.org