These findings are not surprising after a more limited presentation by NSABP investigator Thomas B. Julian at the San Antonio Breast Cancer Symposium in December. Dr. Julian reported findings only for micrometastases detected in the SLN by H&E staining alone.
[Check out our comprehensive coverage of the San Antonio Breast Cancer Symposium.]
The disease-free survival outcome for patients who had micrometastatic sentinel nodes by H&E stain were the same as for those who had positive sentinel nodes. "Macrometastatic patients, on the other hand, had a higher hazard rate of 1.8, which was significantly important," Dr. Julian said.
As for overall survival, "patients who had sentinel nodes with micrometastatic disease had a hazard rate of 0.8 – very similar to those patients who were sentinel-node negative. The P value was insignificant. For those patients who had macrometastases, the hazard rate was 2.4. That was found to be significant," said Dr. Julian, associate director of the breast care center at Allegheny General Hospital in Pittsburgh.
In the published analysis, Dr. Weaver and his associates found that occult metastases were not discriminatory predictors of cancer recurrence. Just 3.6% of the node-negative patients had regional or distant recurrences as first events, and only 30 of these events (in 0.8% of all patients) occurred in patients with occult metastases. All told, 80.5% of patients with occult metastases were alive and free of disease.
"Identification of occult metastases does not appear to be clinically useful for patients with newly diagnosed disease in whom systemic therapy can be recommended on the basis of the characteristics of the primary tumor," the investigators wrote.
The prevalence of occult metastases was significantly associated with age younger than 50 years, clinical tumor size greater than 2.0 cm in the greatest dimension, and planned mastectomy. The authors noted that these findings are not surprising.
"Perhaps the most interesting interaction was with endocrine therapy, indicating that occult metastases are associated with estrogen receptor–positive tumors, a favorable prognostic factor, and that endocrine therapy markedly reduces the risk of a poor outcome," Dr. Weaver and his associates wrote.
They also found that isolated tumor-cell clusters had a smaller effect on outcome than micrometastases for every outcome evaluated, regardless of whether occult macrometastases were included or excluded. The magnitude of difference in 5-year Kaplan-Meier estimates for death from breast cancer was small for detection of isolated tumor-cell clusters vs. no detection (0.6%) and for the detection of micrometastases vs. no detection (2.4%).
The B-32 trial was sponsored by the National Cancer Institute. All of the study authors reported that they have no relevant financial relationships.