ProGastrin Releasing Peptide (ProGRP) is useful for the differential diagnosis of lung masses such as Small Cell Lung Carcinoma (SCLC) vs. Non- Small Cell Lung Carcinoma (NSCLC). It has been reported to be the most sensitive marker for SCLC compared to benign diseases of the lung. Survival in lung cancer mainly depends on histological types and tumor stage. It is important to distinguish SCLC from NSCLC, both of which have different treatment and prognosis. NSE is a more commonly used tumor marker in SCLC but its utility is limited by low sensitivity and specificity. On the other hand, abnormal ProGRP levels are mainly found in lung cancer with the highest concentration in SCLC. ProGRP levels >150pg mL are indicative of SCLC with a probability of 93.7%. The ProGRP sensitivity in SCLC, absence of false positive results in samples with hemolysis, the greater difference between normal ranges ; the levels found in SCLC patients, and normal value in benign diseases (excluding renal failure) support ProGRP as the tumor marker of choice for SCLC. However, ProGRP and NSE are complementary tumor markers and usage of both tumor markers simultaneously increases the sensitivity achieved with ProGRP by 12.7% in patients with limited disease and 14.6% in patients with extensive disease.