Breast Cancer – Pathology
Women’s Center for Breast Health
HOTLINE: 203-789-3244
Normal Structures in the Breast:
The breast is a mass of glandular, fatty, and fibrous tissues positioned over the pectoral muscles of the chest wall and attached to the chest wall by fibrous strands called Coopers ligaments. A layer of fatty tissue surrounds the breast glands and extends throughout the breast. The fatty tissue gives the breast a soft consistency. The glandular tissues of the breast consist of the lobules, which are milk producing glands and the ducts, which are the milk passages. The breast is composed of:
- milk glands (lobules) that produce milk
- ducts that transport milk from the milk glands (lobules) to the nipple
- nipple
- areola (pink or brown pigmented region surrounding the nipple)
- connective (fibrous) tissue that surrounds the lobules and ducts
- fat
Arteries carry oxygen rich blood from the heart to the chest wall and the breasts and veins take de-oxygenated blood back to the heart. The axillary artery extends from the armpit and supplies the outer half of the breast with blood; the internal mammary artery extends down from neck and supplies the inner portion of the breast.
Types of Breast Cancer:
Most breast cancers arise from the cells that line the ducts or cells within the lobules. The most common types of breast cancer begin either in your breast’s milk ducts (ductal carcinoma) or in the milk-producing glands (lobular carcinoma). The point of origin is determined by the appearance of the cancer cells under a microscope. Common breast cancers include:
Ductal Carcinoma In Situ (DCIS): This is the most common form of noninvasive breast cancer and is diagnosed at the earliest time. The tumor cells are still confined within the ducts of the breast. Except in rare cases, the tumor cells in DCIS cannot enter the lymphatic drainage and spread to the lymph nodes or other organs. Treatment for DCIS is primarily aimed at controlling the local site of disease in the breast. DCIS has an excellent prognosis.
Infiltrating / Invasive Carcinoma: Infiltrating or invasive breast cancers spread outside the membrane that lines a duct or lobule, invading the surrounding tissues. The cancer cells can then travel to other parts of your body, such as the lymph nodes or other organs of the body. There are two major subtypes of infiltrating breast carcinoma and are based upon the microscopic appearance of the tumor.
They include:
- Infiltrating or invasive ductal carcinoma (IDC): Infiltrating ductal carcinoma accounts for about 70 percent of all breast cancers. The cancer cells form in the lining of your milk duct, then break through the ductal wall and invade nearby breast tissue. The cancer cells may remain localized or stay near the site of origin or it may spread (metastasize) throughout your body via your bloodstream or lymphatic system. There are also rare subtypes of invasive ductal carcinoma such as tubular, mucinous, medullary and papillary.
- Infiltrating or invasive lobular carcinoma (ILC): Although less common than infiltrating ductal carcinoma, this type of breast cancer invades in a similar way. It starts within the milk-producing lobules and then breaks into the surrounding breast tissue. Infiltrating lobular carcinoma can also spread to more distant parts of your body. With this type of cancer, you typically won’t feel a distinct, firm lump but rather a fullness or area of thickening.
All newly diagnosed cases of infiltrating breast cancer are graded and tested for estrogen receptor (ER), progesterone receptor (PR), and HER2/neu. The values of ER, PR, and HER2/neu are important in choosing treatment options. Treatment of infiltrating breast carcinoma is aimed at controlling the local site of disease in the breast, as well as preventing or limiting spread of disease to sites outside the breast.
Tumor grade:
If the cancer is an invasive type, the pathologist assigns it a grade. The grade is based on how closely cells in the sample tissue resemble normal breast tissue under the microscope. The grading information, along with the cell type, helps your doctor determine treatment options.
Breast cancers are graded on a 1 to 3 scale:
- Grade 1. The cells still look fairly normal (well differentiated).
- Grade 2. The cells are somewhat abnormal (moderately differentiated).
- Grade 3. The cells have lost their proper structure and function (poorly differentiated).
The pathologist determines the grade by looking at the size and shape of both the cell and its nucleus and counting how many cells are in the process of dividing. A higher grade suggests a faster growing cancer that’s more likely to spread.
Hormone receptor status:
Breast cancers are tested for the presence of estrogen and progesterone receptors. A receptor is a protein on the outside of a cell that can attach to specific chemicals, hormones or drugs traveling through the bloodstream.
Normal breast cells and some breast cancer cells have receptors that bind to the female hormones estrogen and progesterone. The hormones signal the cells to increase or “turn on” cell growth.
Breast cancers can be hormone receptor (HR) positive or HR negative. Tumors found to be HR positive are further categorized as estrogen receptor positive (ER positive) or progesterone receptor positive (PR positive). With ER positive or PR positive breast cancer, hormone-blocking medications, such as tamoxifen or Arimidex, slow the cancer’s growth. Hormone receptor positive cancers typically grow more slowly than do HR negative cancers.
HER-2 status
Knowing if a cancer has too many copies of the HER-2 gene also influences treatment decisions. This gene drives production of the growth-promoting HER-2 protein. About one out of every five breast cancers is HER-2 positive, meaning these cancers have greater than normal amounts of the HER-2 protein. These cancers tend to grow and spread more aggressively than do other cancers.
Two sophisticated lab tests can detect HER-2 in cancer cells:
- Immunohistochemistry. Special antibodies that attach to HER-2 protein are applied to the tissue sample, and cells change color if too many HER-2 protein receptors are present.
- Fluorescent in situ hybridization (FISH). Fluorescent pieces of DNA find extra copies of the HER-2 gene. Some laboratories use FISH only, since many breast cancer specialists believe this test is more accurate than is the immunohistochemistry test.
HER-2 positive breast cancers can be treated with drugs that specifically target the HER-2 protein, such as trastuzumab (Herceptin®) and lapatinib (Tykerb®).
Breast cancers that are HER-2 negative and also lack receptors for estrogen and progesterone are referred to as “triple negative.” This form of the disease tends to be aggressive and may respond better to different treatments. It appears to be more common in young black and Hispanic women.
Page last updated on Mar. 09, 2010