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Hidden Lymph Node Metastases Have Small Effect on Breast Cancer Outcomes

Among women with early breast cancer and a sentinel lymph node that appears to be cancer-free on routine evaluation, more extensive lymph node evaluation identifies small areas of cancer in approximately 16% of women. These small, hidden areas of cancer appear to have only a small effect on cancer outcomes, suggesting that current approaches to lymph node evaluation are adequate. These results were published in the New England Journal of Medicine.

For women with early breast cancer, determining whether the cancer has spread to the axillary (under the arm) lymph nodes is an important part of cancer staging. Evaluation of the axillary nodes may involve either an axillary lymph node dissection (ALND), in which many lymph nodes are surgically removed and evaluated, or a less extensive procedure known as a sentinel lymph node biopsy.

Sometimes, very small areas of cancer may be missed on routine lymph node evaluation. These areas of cancer are referred to as “occult” (hidden) metastases. Some previous studies have found that breast cancer patients with occult lymph node metastases have worse outcomes than patients with lymph nodes that are truly cancer-free.

To further evaluate the importance of occult lymph node metastases, researchers evaluated information from the NSABP-B32 study. The primary objective of the study was to evaluate the safety and effectiveness of sentinel lymph node biopsy, but researchers have also been able to explore other questions, including the impact of occult metastases.

The current analysis focused on 3,887 women with sentinel lymph nodes that were negative (cancer-free) on routine evaluation. These lymph nodes underwent further evaluation in an effort to detect occult metastases.

  • Occult metastases were detected in 16% of patients.
  • The presence of occult metastases was linked with a higher rate of recurrence and worse survival, but these effects were small. Five-year overall survival, for example, was 94.6% among women with occult metastases and 95.8% among women without occult metastases.

The researchers conclude that although occult metastases appear to influence breast cancer outcomes, the magnitude of the effect is very small. Efforts to detect occult metastases appear unlikely to provide much benefit. The researchers note that continued follow-up is warranted, and it remains possible that these results will change as more information becomes available.  

Reference: Weaver DL, Ashikaga T, Krag KN et al. Effect of occult metastases on survival in node-negative breast cancer. New England Journal of Medicine. Early online publication January 19, 2011.