ProGRP - Progastrin-releasing peptide
The assay is used to aid in the differential diagnosis in lung cancer and in the management of patients with small cell lung cancer in conjunction with other clinical methods. The results must be interpreted in conjunction with other methods in accordance with standard clinical management guidelines.
Gastrin-releasing peptide (GRP) is an important regulatory molecule that is implicated in a number of physiological and pathophysiological processes in humans. It is a gut hormone and the mammalian counterpart of amphibian bombesin, originally isolated from porcine stomach and widely distributed throughout the mammalian nervous system as well as the gastrointestinal and pulmonary tract. Its 148 amino acid preproprotein, following cleavage of a signal peptide, is further processed to produce the 27 amino acid GRP and the 68 amino acid ProGRP. Due to its short half-life of 2 minutes it is not possible to measure GRP in blood. Therefore, an assay for the measurement of ProGRP (31‐98), a carboxy-terminal region common to three types of human ProGRP splice variants, was developed and it was proven that serum ProGRP (31‐98) levels serve as a reliable biomarker in small cell lung cancer (SCLC) patients.
ProGRP and neuron-specific enolase (NSE) are two molecules which are associated with neuroendocrine derived tissues and tumors. Increased levels of ProGRP have been reported in several neuroendocrine-derived tumor types, including small cell lung cancer, carcinoids, undifferentiated large cell carcinomas of the lung with neuroendocrine features, medullary thyroid carcinoma, other neuroendocrine malignancies, and in a subset of androgen-independent prostate cancer with neuroendocrine features.
ProGRP in benign diseases:
ProGRP serum concentrations between 2 and 50 pg/mL are considered normal in the literature. However, in a study on patients with benign diseases (excluding those with renal failure) including liver diseases, abnormal ProGRP serum levels > 50 pg/mL were found in 2.5 % of the patients. All levels were < 80 pg/mL. Renal failure was the only source of important increases in levels of this biomarker. Elevated levels of ProGRP are highly specific for SCLC, and ProGRP has been reported to be the most sensitive biomarker for SCLC compared to benign diseases of the lung.
ProGRP in lung cancer:
ProGRP has been reported as a specific biomarker for SCLC, but abnormal levels may be found in a small subset of non-small cell lung cancer (NSCLC) patients. These concentrations are significantly lower than the ProGRP serum levels found in SCLC patients. ProGRP serum levels correlate with tumor stage.
ProGRP in differential diagnosis of lung cancer:
High levels of ProGRP (> 120 pg/mL) found in lung cancer patients (without renal failure) indicate a high probability of SCLC.
ProGRP in malignancies other than lung cancer:
Elevated ProGRP serum levels are mainly found in patients with SCLC or neuroendocrine tumors. An elevated ProGRP level in patients with well- differentiated neuroendocrine tumours indicates a primary tumour in the lung and is a factor for poor prognosis. Slightly elevated serum ProGRP levels were found in patients with other malignancies without renal failure, but 99.7 % of them had levels < 100 pg/mL. Using a cutoff of 150 pg/mL as one of the criteria, ProGRP predicted a diagnosis of SCLC with a sensitivity of 72.5 %.
ProGRP in monitoring SCLC patients:
Several investigators have reported that ProGRP is helpful in therapy monitoring of SCLC patients and for the detection of recurrent disease. ProGRP is suggested as the biomarker of choice in SCLC. This is supported by
▪ the sensitivity of ProGRP in SCLC, as well as its specificity in other malignancies,
▪ the normal values seen in most diseases, excluding renal failure and
▪ the absence of false positive results resulting from hemolysis, in addition to the increased discrimination between the normal range and the levels found in SCLC patients. NSE can be a complementary biomarker in SCLC and combining NSE and ProGRP results in enhanced precision in the histological diagnosis, prognosis, and follow-up.
ProGRP is elevated in early stage SCLC. However as the incidence of SCLC in the general population is low, ProGRP assay testing is not recommended as a screening procedure in the general population.
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