New Abdominal Mass After Surgery for Gastrointestinal Stromal Tumor: Desmoid-Type Fibromatosis Difficult to Distinguish from Mesenchymal Tumor - A Case Report.

A new lump in patients with a history of gastrointestinal stromal tumor (GIST) may indicate resistance to medication and recurrence. It is important to monitor for recurrence or metastasis after surgery for GIST, especially in cases of high-risk GIST, as it determines the subsequent treatment. However, it is difficult to differentiate between GIST and DF by imaging. Tissue biopsy and final diagnosis through pathological analysis are usually required. Here, we report 2 cases of primary diagnosis with high-risk GIST and suspected tumor recurrence during Imatinib treatment. The mass was not located where the previous GIST lesion had been. After the complete excision of the mass through laparoscopic surgery, the pathological findings revealed that it was not a recurrence of GIST, but a desmoid-type fibromatosis.