Features of placenta-like alkaline phosphatase (PLAP):
(1) activity resistant to heat treatment (incubation at 56°C or 65°C), heat-stable
(2) mobility during electropheresis
(3) inhibition by different amino acids
(4) precipitation by antibodies to placental alkaline phosphatase
(5) cleavage by neuraminidase
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Name of Patient
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Features
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Regan (lung cancer)
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inhibited by L-phenylalanine
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Nagao
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features of Regan isoenzyme plus inhibited by L-leucine, sensitive to EDTA, slower migration in starch gel
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Other forms: Magoo, Kasahara, Timperley
Tumors showing PLAP include:
(1) seminomas or dysgerminomas
(2) lung cancer
(3) pancreatic cancer
(4) endometrial and other adenocarcinomas of the female genital tract
(5) squamous cell or adenosquamous carcinoma of the cervix
(6) breast cancer
(7) urinary bladder
(8) malignant melanoma
(9) myeloma
(10) malignant lymphoma
(11) gastrointestinal tract
(12) thymoma
In tumors producing PLAP:
(1) The concentration in serum or other body fluids increases with stage.
(2) The concentration decreases with successful therapy.
(3) The alkaline phosphatase can be demonstrated on immunohistochemistry.
Differential diagnosis: elevated alkaline phosphatase isoenzyme associated with metastases to liver and/or bone.
