Effects of oxygen tension on tumor colony formations assessed by human tumor clonogenic assay.

To clarify the effects of oxygen tension on colony formation of fresh human tumor cells, we examined 25 fresh human tumor samples (sixteen gastric cancers, three colon cancers, three breast cancers, one esophageal cancer, one leiomyosarcoma and one malignant lymphoma), using the human tumor clonogenic assay (HTCA) technique. Three different oxygen tensions (2 per cent, 5 per cent, 20 per cent) were tested. At 5 per cent O2, which is considered to be physiological oxygen tension, 19 out of 26 tumors (13/16 in gastric cancer, 2/3 in colon cancer, 1/3 in breast cancer, 1/1 in esophageal cancer, and 1/1 in leiomyosarcoma) showed significant increases of plating efficiencies as compared to those at 20 per cent O2. On the other hand, decreases in plating efficiencies were observed at 2 per cent O2 in seven out of 12 tumors as compared to 20 per cent O2 and eight out of 12 tumors, as compared to 5 per cent O2.