Changes in neutrophil alkaline phosphatase patterns in a case of chronic myelomonocytic leukemia

In neutrophils from a 75-year-old woman suffering from chronic leukemia, an abnormal alkaline phosphatase (ALP) was observed, characterized by a significant increase in neutrophil alkaline phosphatase (NAP) activity, associated with an ectopic expression of two isoenzymes: a thermolabile ALP similar to the early placental form (or non-Regan variant), and a heat-stable isoenzyme closely related to the Nagao isoenzyme. The presence of these oncodevelopmental NAP isoenzymes in a myeloproliferative syndrome has previously not been reported.