GRP (Gastrin Releasing Peptide) is a hormone that is secreted from Small Cell Lung Cancer (SCLC) cells.

Although detection of serum GRP has been expected to be useful for diagnosis of SCLC, determination of serum GRP has not been feasible owing to its instability in blood. The precursor Pro Gastrin Releasing Peptide (ProGRP) however, is more stable and can be used as a serological marker for GRP. The CanAg ProGRP EIA kit measures ProGRP (31-98) a carboxy-terminal region common to human ProGRP splice variants. 

ProGRP is expressed in neuroendocrine-derived tissues and tumors, including small cell lung cancer carcinoids, undifferentiated large cell carcinoma of the lung with neuroendocrine features, medullary thyroid carcinoma, and other neuroendocrine malignancies. Serum levels of ProGRP have been shown to be elevated in a high proportion of patients diagnosed with SCLC while normal levels are found in patients with benign disease. 

Due to its high sensitivity and specificity for SCLC, ProGRP has shown clinical utility in the differential diagnosis of lung cancer. Additive information in the diagnosis of SCLC is provided by the combined measurement of ProGRP and NSE. ProGRP is also useful in monitoring the response to therapy and for the detection of recurrent disease.

Elevated levels of ProGRP may be detected in early stage small cell lung cancer. However, as the incidence of SCLC in the general population is low the ProGRP assay should not be used as a screening test.

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