Use of tomographic nuclear medicine procedures, SPECT and pinhole SPECT, with cationic lipophilic radiotracers for the evaluation of axillary lymph node status in breast cancer patients.

Scintimammography with the cationic lipophilic (99m)Tc-tetrofosmin and (99m)Tc-methoxyisobutylisonitrile (MIBI) is one of the most widely available non-invasive imaging methods employed in the preoperative evaluation of breast cancer axillary lymph node status, for which, at present, axillary lymph node dissection (ALND) is still considered the method of choice. Comparative studies have demonstrated that single-photon emission computed tomography (SPECT) acquisition significantly improves the sensitivity and accuracy achieved with planar scintimammography, particularly when lymph nodes are non-palpable, small in size and limited in number. Thus, SPECT should be preferred to planar imaging, particularly in those patients without clinical suspicion of axillary metastatic involvement, given its high negative predictive value; however, false negative results have been reported due to the small size of lymph nodes and/or to partial or micrometastatic involvement. SPECT could also find clinical application in combination with radioguided sentinel lymph node (SLN) biopsy, providing additional useful information in selected cases. The performance of SPECT can be improved by using a pinhole collimator (pinhole SPECT), as recently demonstrated in comparative studies, and this method also determines the number of lymph nodes, thus delivering important prognostic information. Moreover, pinhole SPECT, the principal limitation of which (as with imaging methods) lies in its inability to detect micrometastases, has also proved capable of increasing the accuracy of radioguided SLN biopsy. However, only limited data relating to pinhole SPECT are available as yet, and clinical trials are necessary to validate its potential value.