Table 1.

Summary of clinical data

Blood donors	Donors, Δ	Donors with circulating epithelial cells, n	Average number of epithelial cells per blood sample (±SD)
Controls (healthy individuals)	13	7	1.5  ±  1.8
Breast cancer patients
No detectable spread	14	13	15.9  ±  17.4
Spread to local lymph nodes only	5	5	47.4  ±  52.3
Distant metastases	11	11	122  ±  140
Total patients	30	29	56.9  ±  98.2
Prostate cancer patients
No detectable spread	3	3	16  ±  4

Flow cytometry was used to analyze the positive events obtained from 20 ml of blood from control individuals; from women with breast carcinoma, or from men with prostate cancer. The numbers of epithelial cells in the blood of the controls are statistically different by t test (P ≤ 0.01) and by Kruskal–Wallis nonparametric analysis (P < 0.001) from each of the three groups of the breast cancer patients and the prostate cancer patients. The data in this table were used to establish a preliminary cut-off value for positive samples. This value was determined by averaging the number of circulating epithelial cells in the normal controls (n = 13) and then adding three times the SD. The average (n = 13) was 1.5 and the SD is 1.8. Cut-off: 1.5 + 5.4 = 6.9. There is no statistical difference between male and female controls.