Shankar S et al. (2005) Gastrointestinal stromal tumor: new nodule-within-a-mass pattern of recurrence after partial response to imatinib mesylate. Radiology 235: 892–898

Little is known about patterns of recurrence in gastrointestinal stromal tumors (GISTs) treated with the receptor tyrosine kinase inhibitor imatinib mesylate (Gleevec® [previously Glivec®], Novartis, New York, NY). Shankar et al. have recently described an indicator of GIST disease progression that, to the knowledge of the authors, is previously unreported: a new nodule within an existing mass.

Participants of a clinical trial of imatinib mesylate for metastatic GISTs (n = 92) were followed up over a 29-month period. All patients underwent contrast-enhanced CT of the chest, abdomen and pelvis at 6-week intervals, and positron emission tomography of the trunk every 6–12 weeks. Liver MRI was performed every 3 months in 15 patients, and unenhanced CT was performed in 6 patients, where these procedures were medically indicated. The images were evaluated for evidence of recurrent GISTs, including new tumors, changes in lesion size, and other conspicuous features.

Disease progression was observed in 39 of the trial participants after variable periods of response to therapy (median 14.4 months, range 2–24 months), and 54% of these had a nodule within a mass, confirmed as recurrent disease by needle biopsy, surgical resection, or follow-up imaging. All patients with these nodules demonstrated progression from single to multiple nodules, and growth of lesions from the initial 2 mm–1.4 cm, during the follow-up period. Other indicators of recurrence included new tumors (7 out of 39 patients [18%]) and growth of existing lesions (20 out of 39 patients [51%]). The group concluded that a nodule within a mass is a reliable indication of GIST recurrence after an initial response to imatinib mesylate.