Imaging Technique Helps Predict Breast Cancer Spread Before Surgery
Breast Cancer and PET Scans
Whole-body positron emission tomography (PET) scans could help physicians determine whether breast cancer has spread to the lymph nodes in the armpit prior to surgery, according to a report in the August issue of the Archives of Surgery, one of the JAMA/Archives journals.
Breast cancer is the most common type of malignant cancer in U.S. women, according to background information in the article. The most reliable way for physicians to determine the prognosis of women with the disease is to determine whether cancer has spread to the axillary lymph nodes, small oval structures in or near the armpits. In procedures known as dissection or biopsy, physicians remove all or part of the lymph nodes nearest the breast to determine whether the cancer has metastasized (spread). "A technique to identify positive lymph nodes before surgery would have several advantages," the authors write.
Alice Chung, M.D., and colleagues at the Cedars-Sinai Medical Center, Los Angeles, evaluated such a technique in 51 women (average age 54 years) who had 54 cases of invasive breast cancer as determined by biopsies. Before their surgeries or chemotherapy, the women had all had PET scans, in which a material similar to glucose (fludeoxyglucose F 18, or FDG) was injected into the body along with a chemical tracer. Because cancer cells use more glucose, they absorb more of the FDG. The researchers analyzed the scans to determine the standardized uptake value for each patient, a number that indicated how much of the FDG was absorbed in reference to how much was injected.
The PET scans indicated activity in the axillary area for 32 (59 percent) of the breast cancer cases. The standard uptake value ranged from .7 to 11; 20 tumors had a value of 2.3 or greater, while 34 had a value of less than 2.3. For further analysis, the researchers set the standard uptake value threshold at 2.3, meaning that cancers with a higher value were considered to have spread to the lymph nodes. Using this threshold, the scans were 72 percent accurate; had a sensitivity of 60 percent, meaning that 60 percent of those with axillary metastases were identified; a specificity of 100 percent, meaning that no one without metastases was identified as having metastases; and a positive predictive value-or proportion of patients with a positive result who are accurately diagnosed-of 100 percent.
Physicians should not necessarily replace other methods with PET scans, but if the scans are already performed before surgery, calculating a standard update value for axillary activity will help them determine if the lymph nodes are involved, the authors write. Technical and calibration factors cause variations in readings, therefore, "each PET center needs to develop its reference values," they continue. "However, if a PET standardized uptake value is validated and can predict node positivity with 100 percent specificity, chemotherapy can be initiated or a surgeon can proceed directly to axillary lymph node dissection for locoregional control." (Arch Surg. 2006;141:783-789)