It is generally accepted that stage I and II breast cancer does not require staging for distant metastases. Stage II is divided into stage IIA and stage IIB based on tumor size and whether it has spread to the axillary lymph nodes (the lymph nodes under the arm). In stage IIA, the cancer is either not larger than 2 centimeters and has spread to the axillary lymph nodes, or between 2 and 5 centimeters but has not spread to the axillary lymph nodes. In stage IIB, the cancer is either between 2 and 5 centimeters and has spread to the axillary lymph nodes, or larger than 5 centimeters but has not spread to the axillary lymph nodes. Whether axillae are involved is determined by physical exam, nodal dissection or, more recently, by sentinel node procedures or imaging and/or biopsy. It is tempting to use PET ro find lymph node invovlement but, unfortunately, PET is not very good for this purpose.
The sensitivity of PEt to stage axillae is limited. A multicenter trial cast doubt on the early supportive studies, and more recent single-center trials performed in the era of sentinel lymph node mapping showed that, compared with sentinel lymph node biopsy, the sensitivity of FDG PET and PET/CT for axillary nodal metastases was as low as 20%–40%. Therefore, PET should not be used as an axillary staging modality
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