Recently, numerous studies on the detection of tumor cells in the peripheral blood have been made from the view-points of diagnosis, prognosis and evaluation of therapeutic effects. The incid ence of tumor cells in the peripheral blood varies widely, ranging from less than 1 % to 96.5% (Table 1). An extensive review of the literature has indicated that this great diversity might be attributable mainly to differences in the criteria for the recognition of malignant cells rather than in the techniques for tumor cell isolation. There fore, it would be important to select the technique which is excellent in both reproductivity and cell preservation. In the present study a dextran sedimentation and smearing technique was selec ted for the detection of tumor cells in the circul ating blood, and this procedure was evaluated by the tumor cell recovery test, using human cance rous ascites cells, stained and unstained (Table 2). The results indicated that the dextran sedi mentation technique possessed an advantage in well preserving the cell morphology, but, the recovery rate, as described in the previous literature, was rather low as compared with those by other methods.
By the use of the dextran sedimentation techni que, tumor cells appearing in the peripheral blood from 130 subjects, which comprised 30 healthy subjects, 38 noncancerous patients, 45 patients with carcinomas and 17 with sarcomas (Table 3), were observed with a care of ruling out the cells which were not usually observable in the peripheral blood.
1. There were found even in the samples from healthy subjects a relatively good number of benign cells such as erythroblasts, immature granulocytes, large mononuclear cells which possi bly would be atypical lymphocytes, monocytes, plasmocytes and their mitotic figures (Table 4).
2. Large histiocytes were seen in 8 cases (6.2%) and occasionally became signet ring cells which might be apt to be confused with tumor cells. Endothelial cells were also seen in 7 cases (5.4%).
3. Megakaryocytes may not infrequently be confused with tumor cells for their large size (Table 5), clumping of the nuclear chromatin, and irregularity in the nuclear membrane. Mega - karyocytes were found at a high frequency (87 %) of healthy subjects, and increased in number in patients with various diseases (Table 6), especially, in patients with disseminated cancers (Table 7 and 8).
4. In the present study tumor cells were dete cted in only 3 patients (6.7%) with disseminated cancers and in 6 patients (35.3%) with sarcomas (Table 9). All patients expired within 5 months after the first detection of tumor cells in the peripheral blood.
