Placental alkaline phosphatase in tumour tissue and serum

Using immunochemical techniques, alkaline phosphatase isoenzymes were determined in tissue samples of breast carcinomas and carcinomas of the gastrointestinal tract. In breast carcinomas only 19% of the patients expressed significant placental alkaline phosphatase activity, compared with 78% in gastrointestinal tumours. The intestinal isoenzyme was found in 50% of the breast carcinomas and in nearly all of the other examined tissues. The two isoenzymes usually represent 1% of the total alkaline phosphatase activity, but in a few cases they may constitute between 10 and 90%. In the serum of the patients under examination, elevated total alkaline phosphatase activity was found in only 7%, and elevated placental alkaline phosphatase in 6% of the cases. No cases of elevated serum intestinal alkaline phosphatase were found. We therefore consider that serum placental alkaline phosphatase is a poor tumour marker for a general screening.