REPLY:

The use of ^99mTc-labeled nanocolloid for sentinel node lymphoscintigraphy in breast cancer has been extensively validated in the literature, as recently reviewed by Nieweg et al. (1). The wide use of this radiopharmaceutical is related to its particle size, which varies from 5 to 80 nm, enabling adequate migration from the injection site and lymph node uptake (2). In our study (3), in only 39% of the patients with lymph node visualization, a single lymph node was visualized during lymphoscintigraphy performed on the basis of a 20-min dynamic study followed by static images at 30 min and at 2 and 4 h. In 61% of the patients, two to eight lymph nodes were seen, not during the first 30 min, as stated by Mirzaei et al., but in the course of the 4-h study. By documenting lymph channel visualization and sequential lymph node filling, the sentinel node was identified in most of these patients. This was reflected by an average of about 1.5 removed axillary sentinel nodes per patient. Furthermore, in this subgroup of patients, nonaxillary drainage was evident in almost 20% of the cases. Further adjustment of the particle concentration and dosage of ^99mTc-labeled nanocolloid increased the lymph node visualization rate to 99% (75/76 patients with breast cancer) (4). This approach led to significantly increased uptake in the sentinel node in relation to second-echelon lymph nodes and improved the lymph channel visualization rate to 53%.

The particle size of the radiopharmaceutical is the subject of much discussion. The use of large particles has been associated with insufficient penetration into lymphatic capillaries (2). Despite this fact, some groups prefer large-particle tracers to minimize the number of radioactive lymph nodes in the axilla. However, this also may lead to an underestimation of the number of sentinel nodes. By visualizing afferent lymph channels on scintigraphy and using blue dye during surgery, we have observed that the presence of two or more sentinel nodes in the axilla is not uncommon. As indicated by Alazraki et al. (5), the greater number of lymph nodes accumulating the radiotracer with smaller particle size should not be regarded as a problem because sequential imaging will help to differentiate between sentinel and secondary nodes in both axillary and nonaxillary locations.

Another important issue is the difference in injection site. Intratumoral and peritumoral administration of the radiotracer enables the mapping of both axillary and nonaxillary drainage, whereas subcutaneous or intracutaneous injection limits the study to the superficial mammary lymphatic system, which drains predominantly to the axilla. Because the detection of metastases in the internal mammary nodes may have prognostic significance and therapeutic implications, the staging of the internal mammary chain by lymphoscintigraphy and sentinel node biopsy may be important. Every node must be counted.