Which ALP isoenzyme is most heat stable and associated with lung cancer?

• A. Regan
• B. Nagao
• C. Kasahara
• D. Placental

Answer: (A)

Understanding ALP isoenzymes involves how they behave when heated. Some isoforms are inactivated by heat, while certain tumor-associated variants remain active after heating. The Regan-Lowe (Regan) isoenzyme is a heat-stable, placental-type ALP that is notably found in several cancers, with lung cancer being a classic association. This combination—high heat stability and linkage to lung cancer—makes it the best fit for the described scenario. Placental ALP is also relatively heat-stable but its clinical association is mainly pregnancy, not cancer; the other named variants exist but are less characteristically tied to lung cancer.