ASSESSMENT OF AXILLARY LYMPH-NODE INVOLVEMENT IN BREAST-CANCER PATIENTS WITH POSITRON EMISSION TOMOGRAPHY USING RADIOLABELED 2-(FLUORINE-18)FLUORO-2-DEOXY-D-GLUCOSE

Background: The presence of metastatic tumor cells in the axillary lym ph nodes is an important factor when deciding whether or not to treat breast cancer patients with adjuvant therapy, Positron emission tomogr aphy (PET) imaging with the radiolabeled glucose analogue 2-(fluorine- 18)-fluoro-2-deoxy-D-glucose (F-18 FDG) has been used to visualize pri mary breast tumors as well as bone and soft-tissue metastases. Purpose : This study was undertaken to evaluate before surgery the diagnostic accuracy of PET for detection of axillary lymph node metastases in pat ients suspected of having breast cancer. Methods: Women who were sched uled to undergo surgery for newly discovered, suspected breast cancers were referred for PET imaging of the axilla region. The women were fi rst clinically examined to determine the status of their axillary lymp h nodes (i.e., presence or absence of metastases). Fifty-one women wer e intravenously administered F-18 FDG and were studied by PET imaging. Attenuation-corrected transaxial and coronal images were visually eva luated by two nuclear medicine physicians (blinded to the patient's me dical history) for foci of increased F-18 FDG uptake in the axilla reg ion. All patients underwent surgery for their suspected breast cancers . Axillary lymph node dissection was also performed on all patients wi th breast cancer, with the exception of four patients who received pri mary chemotherapy for locally advanced breast cancer. A single patholo gist analyzed breast tumor and lymph node tissue specimens. Results: T he overall sensitivity (i.e., the ability of the test to detect diseas e in patients who actually have disease) and specificity (i.e., the ab ility of the test to rule out disease in patients who do not have dise ase) of this method for detection of axillary lymph node metastases in these patients were 79% and 96%, respectively. When only patients wit h primary breast tumors larger than 2 cm in diameter (more advanced th an stage pT1; n = 23) were considered, the sensitivity of axillary PET imaging increased to 94%, and the corresponding specificity was 100%. Lymph node metastases could not be identified in four of six patients with small primary breast cancers (stage pT1), resulting in a sensiti vity of only 33%. Axillary PET imaging provided additional diagnostic information in 12 (29%) of 41 breast cancer patients with regard to th e extension of disease to other sites (i.e., other lymph nodes, skin, bone, and lung). Conclusions: PET imaging with F-18 FDG allowed accura te and noninvasive detection of axillary lymph node metastases, primar ily in patients with breast cancer more advanced than stage pT1. Detec tion of micrometastases and small tumor-infiltrated lymph nodes is lim ited by the currently achievable spatial resolution of PET imaging. Im plications: In clinical practice, PET imaging cannot substitute for hi stopathologic analysis in detecting axillary lymph node metastases in breast cancer patients. PET imaging, however, improves the preoperativ e staging of the disease in breast cancer patients and, therefore, mig ht alter therapeutic regimen options.