A new study has reported that breast cancer patients with sentinel lymph node micrometastases who do not undergo axillary lymph node dissection have higher rates of locoregional recurrence (recurrence in the breast, chest wall, or lymph nodes) than those who undergo the procedure.

The study was designed to investigate the impact of axillary lymph node dissection on five-year locoregional recurrence in breast cancer patients with micrometastases or isolated tumor cells in their sentinel lymph nodes. In sentinel lymph node dissection, the first lymph node (or nodes) to which cancer is likely to spread from the primary tumor is removed for biopsy. Axillary lymph node dissection, which is surgery to remove lymph nodes in the armpit, is recommended for breast cancer patients with positive sentinel lymph nodes. However, recent studies have reported that locoregional recurrence rates appear to be low if axillary dissection is omitted.

To conduct the analysis, the authors retrieved data for all early-stage invasive breast cancer patients in The Netherlands who underwent sentinel lymph node biopsy before 2006 and who had either negative lymph nodes, isolated tumor cells, or micrometastases as final nodal status. Micrometastases generally are defined as metastases of 2 mm or less in diameter. The main study endpoint was rate of regional breast cancer recurrence. The study included 857 women with node-negative disease, 795 with isolated tumor cells in the sentinel node, and 1,028 with micrometastases in the sentinel lymph node.

Among women who did not undergo axillary lymph node dissection, the five-year regional recurrence rates were 2.3% for women with negative sentinel lymph nodes, 2.0% for those with isolated tumor cells, and 5.6% for those with micrometastases. Women who did not undergo axillary dissection and who had isolated tumor cells in their sentinel lymph nodes had a higher risk of regional recurrence than women with isolated tumor cells who underwent axillary node dissection, but this result was not statistically significant. On the other hand, women who did not undergo axillary dissection and had micrometastases were 4.4 times more likely to experience a regional recurrence than women with micrometastases who underwent axillary node dissection. Other factors that increased the likelihood of recurrence were doubling of tumor size (a measure of the growth rate), grade 3 (fast growing, proliferative, and aggressive) and negative hormone receptor (ER-/PR-) status. The authors conclude that not performing axillary dissection in patients with sentinel lymph node micrometastases is associated with increased five-year risk of regional recurrence. Axillary dissection is recommended in patients with sentinel lymph node micrometastases and unfavorable tumor characteristics.

Micrometastases in sentinel lymph nodes should normally be treated

There is considerable debate concerning the prognostic significance of sentinel lymph node micrometastases. Some studies have suggested that such metastases do not influence survival and, therefore, that axillary node dissection (which presumably would destroy any micrometastases in the other axillary nodes) is not needed in such cases. Omitting axillary dissection greatly reduces the likelihood of lymphedema and lowers the cost of treatment.

The study results add valuable information to this debate since they are based on a large unselected group of patients in a clinical setting. The study finding that micrometastases, but not isolated tumor cells, have significant potential to increase the risk of local recurrence, suggest that most isolated tumor cells are not able to survive (not a new finding). The study data also highlights the importance of regarding any tumor presence in the lymph nodes of women with aggressive tumors such as triple negative disease (ER-/PR-/HER2-) differently and treating them accordingly.