What are prognostic factors, and what do they have to do with adjuvant therapy?
Prognostic factors are characteristics of breast tumors that help predict whether the disease is likely to recur. Doctors consider these factors when they are deciding which patients might benefit from adjuvant therapy.
Several prognostic factors are commonly used to plan breast cancer treatment:
Tumor size. Prognosis (probable outcome of the disease) is closely linked to tumor size. In general, patients with small tumors (2 centimeters [a little more than three-quarters of an inch] or less in diameter) have a better prognosis than do patients with larger tumors (especially those that are more than 5 centimeters [2 inches] in diameter).
Lymph node involvement. Lymph nodes in the underarm are a common site of breast cancer spread. Doctors usually remove some of the underarm lymph nodes to determine whether they contain cancer cells. If cancer is found, the nodes are said to be “positive.” If the lymph nodes are free of cancer, the nodes are said to be “negative.” Breast cancer that is node-positive is more likely to recur than cancer that is node-negative because, if cancer cells have spread to the lymph nodes, it is more likely that they have also spread elsewhere in the body.
Hormone receptor status. Cells in the breast contain receptors for the female hormones estrogen and progesterone. These receptors allow the breast tissue to grow or change in response to changing hormone levels.
Research has shown that about two-thirds of all breast cancers contain significant levels of estrogen receptors. These tumors are said to be estrogen receptor positive (ER+). About 40 percent to 50 percent of all breast cancers have progesterone receptors. These tumors are said to be progesterone receptor positive (PR+).
ER+ tumors tend to grow less aggressively than ER- tumors. The result is a better prognosis for patients with ER+ tumors.
Histologic grade. This term refers to how much the tumor cells resemble normal cells when viewed under the microscope. Tumors composed of cells that closely resemble normal breast cells and structures are called well-differentiated. Tumors with cells that bear little or no resemblance to normal breast cells are called poorly differentiated. Tumors that have “in between” cells are called moderately differentiated. For most types of invasive breast cancer, patients who have tumors with cells that are well-differentiated tend to have a better prognosis.
Proliferative capacity of a tumor. This factor refers to the rate at which the cancer cells divide to form more cells. Cells that have a high proliferative capacity divide more often and are more aggressive (fast growing) than those with a low proliferative capacity. Patients who have tumors with cells that have a low proliferative capacity (i.e., divide less often and grow more slowly) tend to have a better prognosis.
Scientists estimate the proliferative capacity of the tumor using such tests as flow cytometry, which includes the S-phase fraction measurement. The S-phase fraction is the percentage of tumor cells that are dividing. Tumors with a high S-phase fraction tend to have an increased risk of recurrence.
Oncogene activation. The activation of an oncogene (a gene that causes or promotes unrestrained cell growth) can make normal cells become abnormal or convert a normal cell into a tumor cell. Patients whose tumor cells contain an oncogene called HER-2/neu, also called erb B-2, may be more likely to have a recurrence. Some research studies suggest that HER-2/neu may be associated with resistance to certain anticancer drugs; however, more research is needed.