原发GISTs的分级，Fletcher等标准

肿瘤的恶性潜能        肿瘤最大直径（cm）        有丝分裂计数（/50HPFs）    
极低                           <2                            <5                                                               
低度                          2~5                             <5                      
中度                           <5                             6~10   
                               5~10                            <5          
高度                           <5                              >5                     
                                >10                          任意核分裂像  
                              任意大小                         >10       

                  
Proposed Guidelines for the Evaluation of GIST Malignancy(from Miettinen et al., Hum Pathol 33:478-483, 2002)

                                Stomach                   Intestine

Probably benign             ≤5 cm and                   ≤2 cm and
                       <5 mitoses/50 HPFs             <5 mitoses/50 HPFs 

Probably malignant         >10 cm or                     >5 cm or
                       >5 mitoses/50 HPFs              >5 mitoses/50 HPFs

Uncertain or low          >5 cm but ≤10 cm and      >2 cm but ≤5 cm and
Malignant potential     <5 mitoses/50 HPFs             <5 mitoses/50 HPFs