Although there are those who recommend routine surveillance for this difficult to follow cancer(Choi et al), unfortuntely, prospective data and a consensus for guidelines concerning the screening of asymptomatic high risk patients and surveillance following multidisciplinary treatment do not exist for GIST. NCCN does not recommend routine surveillance after treatment of GIST.
Consensus meeting for the management of gastrointestinal stromal tumors, Annals of Oncology 2005, Vol. 16, No. 4: 566-578.
nccn.orgt, 2012, Soft Tissue Sarcoma
Grotz TE, Donohue JH. Surveillance strategies for gastrointestinal stromal tumors.J Surg Oncol. 2011 Dec;104(8):921-7..
Haesun Choi Response Evaluation of Gastrointestinal Stromal Tumors The Oncologist April 2008 vol. 13 Supplement 2 4-7
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