A new study presented at the 2011 Breast Cancer Symposium has reported that axillary lymph node dissection in patients with occult sentinel lymph node metastases does not improve survival. Occult sentinel lymph node metastases, which typically are tiny, are metastases not detected during routine examination and pathology. The study further investigated outcomes of participants in the NSABP B-32 trial, which included 5,611 women with invasive breast cancer who were randomly assigned to receive either sentinel lymph node biopsy plus axillary dissection or sentinel lymph node biopsy alone. No significant differences in overall survival or breast cancer-free survival were found between the two groups.

Pathologic assessment of the sentinel lymph nodes was designed to identify all macrometastases greater than 2 mm. This assessment consisted of slicing the sentinel lymph nodes at approximately 2.0 mm intervals, embedding all of the slices in paraffin tissue blocks, and examining one hematoxylin and eosin stained slide per block. Routine use of immunohistochemistry (IHC) or sectioning of deeper levels was not permitted.

Sentinel lymph node tissue blocks from women with sentinel lymph nodes that had been found to be negative were later evaluated for occult metastases deeper in the blocks. The current study evaluated participant outcomes related to occult metastases. Routine and cytokeratin IHC stains were used at two widely spaced additional levels to detect occult metastases, which were found in 15.9% of the participants who had originally been classified as having negative sentinel lymph nodes (616 of 3,884 cases). Of the 616 cases, 431 (69.8%) were found to have isolated tumor-cell clusters, 171 (27.9%) had micrometastases, and 14 (2.3%) had macrometastases. Again, of the 616 occult metastases cases, 316 were in the axillary dissection group (representing 16.4% of the 1,924 patients in this group) and 300 were in the sentinel node biopsy only group (15.3% of 1,960 patients). Non-sentinel node status was available in 312 of 316 patients in the axillary dissection group; 23 (7.4%) were found to have positive non-sentinel nodes.

There were no significant differences in overall survival or disease-free survival between groups among women with occult metastases. There were also no significant group differences in overall survival or disease-free survival in participants who were not found to have occult metastases. The authors conclude that while a more detailed assessment of the sentinel lymph nodes detected a significant level of occult metastases in clinically node negative patients, no survival benefit was seen by the addition of axillary dissection in patients with occult sentinel lymph node metastases.