Breast cancer is the most common cancer in women worldwide, and the leading global cause of cancer death in women. The lifetime risk of breast cancer is approximately 1 in 8. In 2010, more than 1.6 million new cases of breast cancer were diagnosed worldwide.
Breast cancer staging
The prognosis (probable outcome) of breast cancer depends heavily on the stage of breast cancer at diagnosis. Staging is the process of classifying a cancer by four main characteristics: size of the cancer, whether the cancer is invasive, whether the cancer is in nearby lymph nodes, and whether the cancer has spread beyond the breast to other parts of the body.
Breast cancer staging ranges from Stage 0 to Stage 4 (usually expressed in Roman numerals I-IV). Stage 0 is also called ductal carcinoma in situ (DCIS); this is a localized, noninvasive stage where the abnormal cells are still restricted to the breast ducts.
Stage I refers to a tumor 2 cm or smaller that has not spread beyond the breast or has only minimally (small clusters of cells) spread to adjacent lymph nodes.
Stage II refers to tumors between 2 cm and 5 cm that have spread to the axillary (underarm) lymph nodes or tumors larger than 5 cm that have not spread beyond the breast.
Stage III refers to tumors larger than 5 cm that have spread to the axillary lymph nodes or tumors that have spread to the chest wall or skin of the breast.
Finally, Stage IV refers to breast cancer that has spread to other parts of the body, most often the bones and the liver.
Staging guides treatment and predicts breast cancer outcomes
The treatment plan for each individual patient with breast cancer is based on their initial staging. For Stage 0 DCIS, patients are typically treated with breast conserving surgery (lumpectomy), and may be given radiation therapy and/or tamoxifen, a drug which helps block the effects of the estrogen hormone. Patients with Stage I, Stage II and some Stage III cancers usually undergo either lumpectomy or mastectomy (removal of the entire breast), followed by radiation therapy and chemotherapy. Patients with late Stage III and Stage IV cancers primarily receive chemotherapy.
Prognosis (outcome) is also predicted by stage. The 5-year survival rate for patients diagnosed with DCIS is high (93%). However, that survival rate drops to 15% for individuals diagnosed with Stage IV disease.
New blood test may more accurately predict recurrence and survival
While the staging system plays an essential role in guiding therapy, its predictions are far from perfect, particularly when it comes to assessing the risk of recurrence, or reappearance of the breast cancer in other parts of the body. Up to one-third of patients with early stage disease, treated appropriately with surgery and chemotherapy/radiation therapy, experience a recurrence of the cancer at the two-year mark.
Researchers at the University of Texas MD Anderson Cancer Center have developed a new blood test to help identify the patients at risk for these recurrences. This test measures the number of circulating tumor cells in the blood. Cancer cells can dislodge from even small tumors in the breast, and can travel through the bloodstream to ‘seed’ new tumors in other parts of the body including the liver and bones. The researchers discovered that approximately 25% of patients with no other evidence of residual breast cancer had these circulating tumor cells in their blood. The risk of cancer recurrence or death in these patients was approximately four times greater than in patients without the circulating tumor cells. Furthermore, the risk of recurrence increased with the number of cells detected; up to 31% of patients with higher levels of circulating tumor cells relapsed or died during the study period.
Researchers still need to determine exactly how to incorporate this test into a clinical treatment plan. In the long term, this blood test could identify patients with early stage disease who would benefit from more aggressive treatment regimens to improve survival. There may also be future applications in other forms of cancer; research suggests that melanoma survival rates may also be linked to the levels of circulating tumor cells.