Placental alkaline phosphatase (PALP)
Placental alkaline phosphatase (PALP) is one of four isoenzymes of alkaline phosphatase, enzymes that break down organic phosphate esters. Typically, alkaline phosphatase isoenzymes from the liver, bone, and intestine are present in serum, but elevated levels may indicate disease. In non-pregnant individuals, increased PALP levels have been linked to various cancers, including those of the testis, breast, ovary, pancreas, colorectal tract, and lung. Research in the late 20th century focused on PALP and similar proteins as potential tumor markers. Presently, PALP continues to be studied as a valuable indicator for cancer screening and monitoring. Innovative antibody designs aim to detect PALP in tissues and plasma, facilitating more accurate cancer diagnoses and targeted therapies. Notably, PALP has shown effectiveness comparable to established markers like cancer antigen 125 (CA 125) in monitoring ovarian cancer and may indicate recurrence in survivors. While promising, ongoing research is necessary to clarify the full implications of elevated PALP levels in various conditions.
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Placental alkaline phosphatase (PALP)
DEFINITION: Placental alkaline phosphatase (PALP) is one of the four isoenzymes of alkaline phosphatase, a group of enzymes that hydrolyze organic phosphate esters. Alkaline phosphatase isoenzymes associated with the liver, bone, and intestine are normally present in serum. When the serum alkaline phosphatase level is above established reference ranges, determining which fraction is elevated may be helpful in pinpointing the source of disease.
RELATED CANCERS: When pregnancy is not a condition of consideration, elevated levels of PALP have been associated with cancers of the testis, breast, ovary, pancreas, colorectal tract, and lung. In the 1970s and 1980s, researchers investigated the relationship between malignant changes in many tissues and the serum concentration of several fetal-type proteins. They pursued PALP along with alpha-fetoprotein (AFP) and carcinoembryonic antigen (CEA) as tumor markers. Of these, PALP and the PALP-like isoenzymes are still being studied as useful markers for screening or monitoring cancer and related conditions.
Ongoing research: Cancer researchers continue exploring PALP's role as a tumor marker. Antibodies to detect and differentiate PALP and the related PALP-like isoenzymes are being designed and tested. Some antibodies are used in immunohistochemistry protocols, requiring a biopsy of the organ where the suspicious tumor is located. These tissue biopsy studies can confirm the presence of PALP and PALP-like isoenzymes, further characterizing the tumor and leading to a more specific diagnosis and targeted therapy.
Other researchers are designing antibodies that target PALP and PALP-like isoenzymes in an individual’s plasma and thus can serve as noninvasive markers for cancer. Elevated concentrations of PALP and PALP-like enzymes were found to have the same effectiveness as cancer antigen 125 (CA 125) and AFP in monitoring ovarian cancer. However, there is some evidence that PALP and PALP-like isoenzymes may become useful indicators of cancer recurrence in survivors. PALP and PALP-like isoenzymes have shown the most promise in treating seminomas, malignant germ cell tumors that develop in the testes, brain, chest, and abdomen. The development of increasingly sensitive assay tests has allowed doctors to detect levels of PALP in patients with seminomas more easily. Still, more studies are needed to fully understand elevated PALP levels, which could indicate other conditions. Medical researchers continue to investigate the use of PALP as a biomarker for lung and gastrointestinal cancers, but more studies are necessary.
Bibliography
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