Factors that affect treatment decisions and prognosis. A number of factors are used to predict the outlook of successful treatment and the possibility of a cure. They include the following:
Lymph node status
If the cancer is ductal carcinoma in situ (DCIS) or has not spread to the lymph nodes (that is, node-negative), the five-year survival rates with treatment are up to 98%.
It should be noted, however, that cancer recurs in between 9% and 30% of such node-negative cancers. Recurrence is a potentially life-threatening problem, even if the disease relapses locally in the same breast. Nevertheless, in one study, among DCIS patients with locally invasive recurrence, eight-year mortality rates were still only 12%.
If the lymph nodes contain cancer cells (that is, are node-positive), then survival rates fall. If the tumour is larger than 5 cm or there is widespread involvement in the lymph nodes, it is sometimes referred to as locally advanced. In such cases, the survival rate drops to about 75% and below.
Tumour size, grade and type
The location of the tumour within the breast is an important prognostic factor. Tumours that develop toward the outside of the breast tend to be less serious than those that occur more toward the middle of the breast.
Large tumours pose a higher risk than small tumours. Undifferentiated tumours, which have indistinct margins, are more dangerous than those with well-defined margins.
Breast cancer cells may contain receptors, or binding sites, for hormones like estrogen or progesterone. Cells containing these binding sites are known as hormone receptor-positive cells and if they lack them are called hormone receptor-negative cells.
Hormone receptor-positive cells grow more slowly than receptor-negative cells. Women have a better prognosis if their tumours are receptor-positive because these cells grow more slowly than receptor-negative cells and they have more treatment options. (Hormone receptor-negative tumours can only be treated with chemotherapy.)
Researchers are investigating a number of substances in the tumour cells that will indicate whether a cancer is likely to spread or not. Such chemical markers may help physicians determine treatments, and some may even prove to be targeted for future drugs.
One of such markers is the HER-2 protein. This protein is part of the epidermal growth factor receptor family and is becoming an important marker in breast cancer. It is involved in the growth and spread of breast cancer cells, and about 25% to 30% of breast cancer patients have high levels of this protein. The presence of HER-2 may suggest aggressive cancer and is proving to be important in determining treatment choices.
Influence of genes
Determining a “genetic signature” for a tumour may prove to be a very powerful predictor of the aggressive nature of breast cancer. Researchers have focused on 70 genes whose activity patterns may help make such predictions.
The relevance of the inherited BRCA1 or BRCA2 mutations to survival is controversial. Some studies have suggested that these mutations offer a survival advantage, while others suggest that they make no difference or even worsen prognosis. Women with these genetic mutations do have a greater risk for new cancer to develop. Patients with BRCA1 mutations tend to develop tumours that are hormone receptor-negative, which can behave more aggressively.
The more rapidly a tumour grows, the more dangerous it is. A number of tests measure aspects of cancer cell division and may eventually prove to predict the disease. For example, the mitotic index (MI) is a measurement of the rate at which cells divide. The higher the MI, the more aggressive cancer. The cells of another measure at a certain phase of their division.
Tests for metastasis If cancer has metastasized and spread through the bloodstream to other sites (most often the lung, liver and bone), the average survival time for patients treated with chemotherapy is between one and two years (with some patients living for many years). However, there is more hope now and in the future as new combinations of drugs are improving these averages.