A very important way to predict the outcome from breast cancer is to determine whether it has spread to the axillary lymph nodes—small tissue structures under the arms. To test whether cancer is present in these lymph nodes, doctors can perform biopsies and/or dissections, in which some or all of the nodes are removed and studied.

Another less invasive technology, positron emission tomography (PET) scan , may also be used to identify cancer that has spread to the lymph nodes. In this procedure, a glucose-like substance called fludeoxyglucose F 18 (FDG) is injected into the body and the PET scan analyzes how much FDG is absorbed. Since cancerous cells tend to use more glucose, the more FDG that is absorbed, the more likely the tissue contains cancer.

A new study in the August 2006 Archives of Surgery found that PET scans performed on women who were about to undergo breast cancer treatment were 72% accurate in determining whether the cancer had spread to the lymph nodes.

About the Study

Researchers studied 51 women who had been diagnosed with 54 invasive breast cancers. The participants underwent PET scanning before having surgery or chemotherapy to treat their cancer. As part of the PET scans, the researchers calculated a standard uptake value (SUV, a number that indicates how much FDG was absorbed relative to how much was injected) for each participant. The researchers compared the results of the scans to the results of subsequent lymph node biopsies and dissections.

The PET scans identified “axillary activity” in 32 (59%) of the participants. The researchers found that 2.3 was the optimal SUV threshold, meaning that cancers with SUVs of more than 2.3 were considered to have spread to the lymph nodes. Using this threshold, the accuracy of the PET scans in identifying cancer in the lymph nodes was 72%. There were no false positive findings, meaning that cancers that had not spread to the lymph nodes did not have SUVs over 2.3. But only 60% of those with lymph node spread were identified with the PET scan—40% were not.

This study was limited because of its small sample size. Also, the SUV threshold may not apply to other PET scan centers, since differences in scanning techniques result in variable readings. The authors recommend that each PET center develop its own reference values.

How Does This Affect You?

These findings suggest that PET scans have the potential to help doctors determine whether breast cancer has spread to the lymph nodes. This may be especially beneficial before surgery, since identifying cancerous lymph nodes can reduce the risk of needing future surgeries to remove missed cancerous nodes.

But PET scans are not yet accurate enough to replace other techniques, including biopsy and dissection. The authors do not recommend routine PET scanning of all women with breast cancer, but when PET scanning is done and it shows axillary metastases, surgical exploration of the axilla may not be needed. Further confirmation of this data will be needed, though, before the authors’ conclusions can be generally adopted. This study and others indicate that PET scans are most accurate in patients with larger, more aggressive breast cancer tumors. However, as technology improves, PET scans may one day be able to spare some patients of invasive biopsies and dissections.