Italian survey of second tumors in patients with diagnosis of GIST (gastrointestinal stromal tumor)

11032 Background: GISTs are the most common mesenchymal tumors of the digestive tract. As of recent, new links are being made between GISTS and secondary malignancies. However, whether the coexistence of GISTs with other tumors is stochastic, or the result of related pathogenetic mechanisms is still unknown. Methods: We retrospectively reviewed clinical and molecular features from all GIST patients with second tumors treated in seven Italian GIST reference centers. Qualitative variables were compared using the Fisher exact test. Results: Clinical data of 184 patients with diagnosis of GIST were evaluated. Median age at diagnosis was 66 years, KIT exon 11 resulted the most frequent mutation (73%) while seven patients (3.8%) had a genetic syndrome. The most common primary GIST localizations were stomach (54%) and small intestine (33%). Second tumors arose mostly from gastrointestinal and genitourinary tract. Fourtythree patients had two primary tumors other than GIST and five patients had three other primary malignancies. According to Miettinen criteria, 45% of non-metastatic patients at diagnosis belong to low or very low-risk classes. We highlighted a significant correlation (P=0.002) between risk class and second/third tumor localization, with considerably high percentage of GI second malignancies in low/very low risk GISTs (table). Conclusions: The high frequency of second/third tumors reported in low and very low GIST calls for a careful follow-up also in these patients. Furthermore, this population requires further genetic investigation, NGS analysis is ongoing. [Table: see text]