Sentinel Lymph Node Mapping in Breast Cancer

As Dr. Cody points out, sentinel lymph node mapping of axillary nodes in patients with invasive breast cancer will probably become the standard of care for patients with early breast cancer, and will replace standard axillary dissection for many of these patients. With mammography increasing the detection of small, nonpalpable breast cancers, which pose a very low risk of axillary metastases, it is difficult to justify the continued use of standard axillary dissection. To my mind, it is also difficult to justify omitting axillary dissection of any type in these settings.

Those who adopt this approach are correct in asserting that the costs of delivering care to these patients is markedly reduced, as is morbidity. Nevertheless, the admittedly small percentage of patients with positive axillary nodes are done a distinct disservice by not having these nodes removed. Also, due to their small primary tumor size, these patients would not be advised to have adjuvant systemic therapy unless these positive nodes had been removed. Perhaps the widespread use of sentinel lymph node mapping will represent a compromise position accepted by both sides in this disagreement.

Which Patients Should Undergo Sentinel Lymph Node Mapping?

Cody discusses the current state of sentinel lymph node mapping and the remaining controversies surrounding its use. As outlined in Table 3 of his article, this procedure is not the standard of care currently, but rather, according to guidelines developed by the National Comprehensive Cancer Network (NCCN), is considered category 2 (“somewhat controversial”). Patient selection, according to these guidelines, is likely to change as more experience with the technique accumulates.

Patients with T1 and smaller T2 primary tumors and clinically negative axillae are candidates for sentinel lymph node mapping. Ideal candidates are patients at low risk for axillary metastases. Patients with clinically involved nodes or multicentric primary tumors should undergo axillary dissection without sentinel lymph node mapping.

Blue Dye, Radioisotope, or Both?

It is uncertain whether it is ideal to map with blue dye alone, radioisotope alone, or both. As shown in the author’s Table 1, all three approaches have proved successful. Advocates of blue dye alone emphasize its simplicity, avoidance of radioactivity, and lower cost. Proponents of radioactivity (or both, as Cody points out) claim a faster learning curve and, in some hands, increased accuracy.

As illustrated by Cody’s series, a small percentage of patients have sentinel nodes identified by one but not the other technique. For surgeons using both methods, it is reported that both the blue node(s) and radioactive node(s) are removed and that they may not be the same.

Which Staining Technique(s) Should Be Used?

Whether or not to use standard hematoxylin and eosin (H&E) staining alone or to utilize immunohistochemical (IHC) staining with serial sectioning is controversial. Some experts interpret studies showing the presence of micrometastases in axillary nodes as having no prognostic significance; these authors omit IHC analyses. Others, including Cody, believe that the identification and removal of nodes with micrometastases benefit prognosis and therefore include IHC with serial sectioning.

How Much and What Type of Training Are Needed?

There is a consensus among experts about the need for training in the performance of sentinel lymph node mapping and the need to initially compare the histology of sentinel lymph nodes with nodes removed by standard axillary dissection. Agreement has not been reached about how many so-called on-protocol procedures should be done to ensure that a negative sentinel node procedure does not leave a positive node elsewhere in the axilla. Most experts believe that a given surgeon cannot be confident about the accuracy of sentinel lymph node mapping until some histologically positive sentinel nodes are identified.

Also, when IHC is utilized, pathologists need training, and when radioactivity is used, nuclear medicine specialists need training. As Cody points out, this is new ground for these physicians and is unlike whole-organ imaging. Most experts claim that this low level of radioactivity poses little or no risk to operating room and pathology staffs.

Other Controversies

The author discusses the many controversies regarding radioactive isotopes. Ideal particle size (10 to 200 nm) is important; particles that are too heavy do not leave the primary site, and particles that are too small involve multiple nodes or leave the nodal basin so quickly that the sentinel node cannot be identified. Whether particles should be filtered or unfiltered is unclear; both seem to work when used by different groups. The site of injection is also important.

The studies outlined in the author’s Table 5 should provide some answers to these questions. One would predict that identifying a positive sentinel node and not dissecting the rest of the axilla would be detrimental to outcome, but this question is being studied.

Conclusions

To put these controversies into perspective, it should be admitted that axillary dissection currently is not standardized. In the era of radical mastectomy, all patients underwent complete axillary dissection. With the advent of modified radical mastectomy and then breast-conservation techniques, the extent of dissection employed in a “standard” level I-II dissection in patients with clinically negative axillae differs somewhat from surgeon to surgeon. Thus, as sentinel lymph node mapping evolves to assume an important role, similar individual differences are likely to be seen.