Leukocyte alkaline phosphatase activity in patients with malignant disease.

One hundred patients with malignant disease were screened for leukocyte alkaline phosphate (LAP) activity. The new observation made was that patients with malignant disease demonstrate significantly lower levels of LAP than in normal controls. The low LAP activity is present irrespective of primary tumor category, "activity" of disease, or type of therapy. The pattern of metastases may influence LAP activity, in that patients with liver metastases tended to have higher LAP levels. In spite of low baseline LAP levels in patients with malignant disease, the development of secondary infection is associated with elevated LAP levels.