Which ALP isoenzyme is associated with lung cancer?

The Regan isoenzyme of alkaline phosphatase (ALP) is specifically associated with certain malignancies, particularly lung cancer. This isoenzyme is considered an oncofetal antigen, and its presence can indicate the existence of malignancies where other isoenzymes may not be elevated. In cases of lung cancer, the Regan isoenzyme is often detected at elevated levels in the serum, thus serving as a potential biomarker for diagnosis or monitoring of the disease.

In contrast, the other isoenzymes listed serve different physiological roles or are associated with other conditions. For instance, tissue-nonspecific ALP is involved in physiological processes in various tissues, such as liver and bone, and may increase in liver and bone diseases but is not specifically indicative of lung cancer. Bone ALP is primarily associated with bone formation and metabolic processes of the bone, frequently elevated in conditions such as Paget's disease or osteosarcoma. Intestinal ALP is primarily related to the intestines and is relevant in certain gastrointestinal conditions, but it does not have a direct link to lung cancer.

Thus, the Regan isoenzyme is distinctly recognized for its association with lung cancer, making it the correct choice in this context.