Interobserver agreement among endosonographers for staging of pancreatic cancer by endoscopic ultrasound

Endoscopic Ultrasound (EUS) has been reported to be an accurate modality for staging pancreatic cancer (CA). However, there is limited data regarding the effects of interobserver variation on the overall accuracy and clinical utility of EUS for staging pancreatic CA. AIM OF STUDY: To determine interobserver reliability for EUS staging of pancreatic tumors. METHODS: Twelve patients with previously diagnosed pancreatic ductal adenocarcinoma underwent staging with EUS. Surgical correlation was obtained in all patients. A blinded observer developed a study videotape of real-time EUS for each case. The videotape was then distributed to ten endosonographers with at least one year of previous experience who independently reviewed the tape and recorded their interpretation of the EUS tumor stage for each case based upon previously reported EUS criteria for staging pancreatic CA. A multiple observer kappa (k) statistic was calculated for each staging category (T, N, and T+N), vascular invasion and overall k. Kappa accounts for agreement due to chance alone and standardized ranges are available. The Light (G) statistic was utilized to allow for the presence of the gold standard. Accuracy was assessed using a simple matrix format. RESULTS: Overall agreement was highly statistically significant for T stage: k=0.22 ( G=5.52, Z=2.35, p<0.01).Observers were more likely to agree with T3 stage tumors (94%) than T2 (40%) or T1 (33%) lesions. The Overall agreement for N stage was highly statistically significant: k=0.23 (G=4.44, Z=4.90, p<0.01). Agreement for absence of nodal involvement (63%) was better than that for the presence of nodal involvement (56%). For overall staging (T+N): k=0.18 (G=9.19, Z=4.98, p<,01). For vascular invasion: k=0.26 (G=3.90, z=3.33, p<.01). The agreement for T and N stage improved as stage increased (p<0.01) and in the presence of vascular invasion (p<0.01). CONCLUSION: Interobserver agreement is good for staging pancreatic tumors by EUS. However, it appears to be better for some tumor stages than others. Experience may play a role in the successful use of this modality to evaluate pancreatic tumors.