Original Abstract
BACKGROUND: The ninth TNM edition distinguishes single-station (N2a) from multistation (N2b) disease, increasing concern for cross-contamination between N2 lymph nodes during EBUS staging when ROSE is unavailable. The absolute probability and clinical impact of this phenomenon are uncertain. We estimated a theoretical upper bound on false upstaging and the number of needle changes required to prevent one false upstage. METHODS: A Monte Carlo decision model simulated mediastinal staging in 100,000 virtual patients across published estimates of occult N2 prevalence, probability of a single-station involvement, and contamination rates. Outcomes were the probability of false N2b upstaging and the number of additional needle changes needed to prevent one false upstage (NNC). Sensitivity analyses varied the contamination rate, single-station probability, and sampling order. RESULTS: False upstaging in central cN0 disease was ∼0.5% to 0.8% in the base case, increasing to 1.4% in higher-risk scenarios. cN1 disease showed slightly higher probabilities. Needle-change efficiency was low; preventing one false upstage required roughly 250 to 350 extra needle changes in central cN0 and >1000 in peripheral cN0. Sensitivity analysis showed comparable influence of contamination rate, single-station probability, and sampling order. CONCLUSION: The risk of spurious upstaging during EBUS staging without ROSE is small but not negligible, concentrated in central cN0 and cN1 tumors. When ROSE is not available, routine needle change between N2 stations provides minimal benefit for most patients. In cases where ROSE is not available and resources are limited, a selective strategy targeting high-risk contexts may offer the best balance between accuracy and procedural efficiency.