FDG PET/CT points out malignant lymph nodes inside the breast

Poor patient outcomes are associated with primary breast cancer that has metastasized to internal mammary (IM) lymph nodes. Researchers compared F-18 FDG PET/CT with results of cytopathologic testing from image-guided fine-needle aspiration (FNA), revealing a high percentage of proven metastases from positive FDG PET scans, according to a study published in the May  issue of the American Journal of Roentgenology.

Conventional metastatic risk assessment includes information about HER2/ERRB2 growth receptor and hormone receptor status, but recent studies have started paying more attention to IM lymph node involvement, suggesting that it better indicates distant metastases and poor survival.

Carolyn L. Wang, MD, from Swedish Cancer Institute in Seattle, and colleagues devised a retrospective study to evaluate PET/CT risk stratification for women with possible breast cancer metastases to the IM lymph nodes. They conducted a database search to identify 1,259 patients referred for whole-body  PET/CT for initial staging or restaging of breast cancer from January 1, 2005, through December 31, 2010.

“Metastasis in an IM lymph node has the greatest effect on staging when the IM node is the only site of regional lymph node metastasis (negative axillary nodes) in the patient,” the authors wrote.

This has a substantial effect on breast cancer staging, as this classification changes stage II breast cancer to stage III cancer and survival rates projected for these patients automatically drops either 6 or 26 percentage points depending on the starting survival rate, with the poorest prognosis estimated at 41 percent survival.

“Although fewer than 10 percent of breast cancer patients have positive IM nodes on 18F-FDG PET/CT performed for initial staging or restaging, a positive IM node indicates a very high likelihood of malignant involvement on ultrasound-guided FNA,” wrote the authors. “The presences of high tumor grade, [lymphovascular invasion], or triple receptor–negative status are risk factors for IM node positivity on 18F-FDG PET/CT.”

For this retrospective study, a total of 110 patients, or 9 percent, showed F-18 FDG positive IM lymph nodes following FDG PET/CT imaging. FNA was performed for 25 of these patients. A total of 20 IM lymph nodes were found to be metastatic after cytology.

“Our results show that an FDG-avid IM lymph node on PET/CT has a very high likelihood of being malignant because 80 percent of the 25 patients who underwent FNA had positive results for neoplasm,” wrote Wang et al.

Inconsistencies between results of this study and two previous studies were noted. Prior studies showed a higher rate of positive FDG PET/CT scans (one showed 25 percent and another 13 percent) for IM lymph node metastases. This was thought to be due to the previous studies’ exclusion of women being restaged following adjuvant therapy, which has an estimated 1 to 5 percent rate of recurrence.