In their study of the histochemical detection of metastases from breast cancer to bone marrow, Braun et al. (Feb. 24 issue)1 found that multivariate analysis identified the presence of cytokeratin-positive cells in the bone marrow as an independent predictor of survival. What do the authors think about the use of flow cytometry after cytokeratin staining? Their results clearly demonstrate that the presence of cytokeratin-positive cells in the bone marrow of patients with breast carcinoma is associated with shorter survival. However, because cytokeratin-positive cells were detected in control patients with nonmalignant disease and stage I tumors had fewer than 5 cytokeratin-positive cells per 2×10⁶ bone marrow cells, the authors should also clarify the threshold of positivity needed to avoid false positive results. Braun et al. found a median of 3 cytokeratin-positive cells per 2×10⁶ bone marrow cells, but the exclusion of patients with fewer than 3 cytokeratin-positive cells per 2×10⁶ bone marrow cells would not be enough, because the confidence interval for each stage is not mentioned.

• diagnosis
• metastasis
• molecular technique
• bone marrow

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