This observational study is proposed to evaluate if the trend in the levels of cf-DNA evaluated on a sample of peripheral blood may be related to different clinical behaviors of the disease monitored by radiological investigations conducted.

Demetri and colleagues presented, at the AACR and ASCO Annual Meeting 2013, an exploratory analysis to assess GIST genotypes on patients in the GRID study. Mutations in the KIT gene were detected in 58 percent of the blood samples compared with 66 percent of the tumor tissue samples (31). However, when focusing their analysis on secondary KIT mutations, which are the mutations that drive resistance to targeted therapies like imatinib and sunitinib, the researchers found mutations in 47 percent of blood samples compared with only 12 percent of tissue samples. In addition, nearly half of blood samples in which secondary KIT mutations were found, harbored multiple secondary mutations. Therefore, cf-DNA may become an efficient marker of mutational GIST status and disease itself.

On this basis, this trial aims to evaluate whether tumor DNA carrying mutations (for KIT, PDGFRα, BRAF, RAS, SDH) can be detected and quantified in the plasma of patients with GISTs, either with active disease or during follow-up, and whether detection can be correlated with the disease status.

• Male or female patients aged >= 18 years
• Histologically confirmed diagnosis of GIST of any anatomical location either by biopsy or surgical specimen
• Available archival tumor tissue
• Signed informed consent form

Exclusion Criteria:

• Impossibility to ensure adequate clinical and serum sample follow-up
• Serious psychiatric disease that precludes informed consent or limits compliance

The target population includes adult patients with histologically confirmed GIST, either with active disease or in follow-up.