A new prospective study has reported that while undetected micrometastases influence prognosis in patients with sentinel lymph nodes that are initially classified as negative, the magnitude of the difference in outcome at five years is only 1.2%. The study was designed to investigate the impact of occult lymph node metastases (i.e., metastases not detected during routine examination) on survival after a diagnosis of early stage, lymph node negative breast cancer. Previous retrospective and observational studies have reported that occult lymph node metastases influence disease recurrence and survival in women with breast cancer. However, prospective randomized trials have not been performed to date.

In the study, 3,887 breast cancer patients were randomly assigned to receive either sentinel lymph node biopsy plus axillary lymph node dissection or sentinel lymph node biopsy alone. The initial lymph node evaluation was designed to detect all macrometastases larger than 2 mm. Paraffin-embedded tissue blocks of sentinel lymph nodes from patients with pathologically negative sentinel lymph nodes were centrally examined for occult metastases deeper in the blocks. The women's oncologists were not made aware of the findings, and the findings were not used to make treatment decisions.

Occult metastases were found in 15.9% of the study participants. There were statistically significant differences between patients with occult metastases and those in whom no occult metastases were detected with respect to overall survival, disease free survival, and time to distant recurrence. However, five-year overall survival rates for participants in whom occult metastases were detected (94.6%) were similar to those without detectable metastases (95.8%). The authors conclude that the study results do not indicate a clinical benefit of additional evaluation, including immunohistochemical analysis, of initially negative sentinel nodes in patients with breast cancer.