Your doctor suspects that you have breast cancer. To confirm the diagnosis, a pathologist analyzes a tissue sample (biopsy) taken from the lump or suspicious area in your breast. This will tell if you have cancer or some other, benign condition. If the biopsy does show cancer, the results provide your doctor with information about the type of breast cancer and help determine treatment options.
The biopsy results appear on a pathology report, which provides detailed information including the type of breast cancer, if it’s invasive or noninvasive, the tumor grade ? how closely the cancer cells resemble normal tissue ? if the cancer is sensitive to hormonal therapies and if it has too much of a protein called HER-2.
Sophisticated lab tests can also analyze breast cancer tissue for molecular and genetic features of breast cancer cells. Understanding all these aspects of a cancer helps your doctor tailor your treatment plan.
Common types of breast cancer
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.
In situ breast cancer
In situ (noninvasive) breast cancer refers to cancer in which the cells have remained within their place of origin ? they haven’t spread to breast tissue around the duct or lobule. The most common type of noninvasive breast cancer is ductal carcinoma in situ (DCIS), which is confined to the lining of the milk ducts. The abnormal cells haven’t spread through the duct walls into surrounding breast tissue. With appropriate treatment, DCIS has an excellent prognosis.
Invasive breast cancer
Invasive (infiltrating) 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.
* Invasive ductal carcinoma (IDC). IDC 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 ? staying near the site of origin ? or spread (metastasize) throughout your body, carried by your bloodstream or lymphatic system.
* Invasive lobular carcinoma (ILC). Although less common than IDC, this type of breast cancer invades in a similar way, starting in the milk-producing lobules and then breaking into the surrounding breast tissue. ILC 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.
Less common types of breast cancer
Not all types of breast cancer begin in a duct or lobule. Less common types of breast cancer may arise from the breast’s supporting tissue, including the fibrous connective tissue, blood vessels and lymphatic system. In addition, some tumors don’t actually begin in the breast but represent a different type of cancer that has spread (metastasized) from another part of the body, such as the lymphatic system (non-Hodgkin’s lymphoma), skin (melanoma), colon or lungs. These are not called breast cancer but are referred to as cancer from where it started, now metastatic to the breast.
Unusual types of breast cancer include inflammatory breast cancer, phyllodes tumor, angiosarcoma, osteosarcoma, metaplastic breast cancer, adenoid cystic carcinoma and Paget’s disease of the breast. There are also rare subtypes of invasive ductal carcinoma ? tubular, mucinous, medullary and papillary.
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).
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, slow the cancer’s growth. Hormone receptor positive cancers typically grow more slowly than do HR negative cancers.
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. Chromogenic in situ hybridization (CISH) is a similar technique.
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.
Emerging ways to classify breast cancer
The goal of much current breast cancer research is to understand the characteristics of cells in individual tumors. By applying the latest in molecular technology, researchers can identify genes associated with breast cancer and measure their activity in tissue samples. Tools called microarray analysis and reverse transcriptase-polymerase chain reaction (RT-PCR) are used to study patterns of behavior, or expression, of large numbers of genes in breast tissue samples. The researchers can then identify a set of genes whose activity provides information about a cancer, such as the likelihood of recurrence. These tests, known as genetic profiling or gene-expression profiling, have so far been used only for a minority of breast cancers.
Some researchers have proposed a new way to classify breast cancers based on molecular features rather than on the cancer’s appearance under a microscope. These types include:
* Luminal A and luminal B. The genetic activity of these cancers is similar to that of normal lumen cells ? those that line the breast ducts and glands. Luminal cancers are estrogen receptor positive and usually grow slowly.
* HER-2. These cancers have extra amounts of HER-2 protein and extra copies of the gene. They tend to grow quickly but respond well to treatment with Herceptin.
* Basal. Basal breast cancers contain normal amounts of HER-2 and lack estrogen and progesterone receptors. This type of cancer grows rapidly.
Most doctors still use the traditional categories when talking about types of breast cancer. But they draw on the latest research about breast cancer features to determine the best course of treatment.