Geometrical Measurement of Central Tumor Location in cT1N0M0 NSCLC Predicts N1 but Not N2 Upstaging

EBUS‐TBNA for mediastinal staging of centrally located T1N0M0 non‐small cell lung cancer clinically staged with PET/CT

“…Actually, the prevalence of occult N2 disease in tumours classified as cT1N0 is low, regardless of the location (central or peripheral), ranging from 4.6% to 8% in different series. [22][23][24] In the setting of our series, the prevalence of occult N2 (5.1%) is similar to that of other series exclusively including patients with cT1N0 tumours but lower than in overall patients with normal mediastinum on PET/CT. This finding explains the NPV of our study since NPV is related with prevalence.…”

“…Patients with tumours with normal mediastinum on PET/CT and an indication for invasive staging include a wide population with different prevalence rates of occult N2 disease, ranging from 26%-40.7% in patients with N1 on PET/CT, 6,20 to 11%-22% in patients with tumours sized >3 cm 10,21 or 4.6%-6.4% in patients with central T1N0 tumours. 10,22 Moreover, central cT1N0 tumours or peripheral cT2N0 or cT1N1 tumours are difficult to find in clinical practice while tumours sharing the three characteristics (e.g., central T2N1 tumours), with an added risk of occult N2 disease, are commonly seen. Therefore, the prediction of risk of N2 in patients with normal mediastinum on PET/CT in clinical practice is difficult to estimate, although there are two apparent patterns: high likelihood of occult N2 disease in cN1 and low likelihood in cT1N0.…”

Response

“…We would like to thank Sanz-Santos et al for their comments on our publication. 1 The authors expressed two concerns: (1) quantitative methods of tumor location suggested by DuComb et al 2 (three-dimensional coordinates and carina-to-cancer distance) and Sanz-Santos et al 3 (inner margin ratio and outer margin ratio) were not analyzed and (2) the starting point of the location index is ambiguous.…”

“…First, both of the quantitative methods mentioned by Sanz-Santos et al were not associated with mediastinal lymph node metastasis in their studies. 2,3 Given that the purpose of our analysis was to reveal clinically useful and robust definitions for central lung cancer, the candidate methods of tumor location were chosen if there was any evidence for potential association with nodal disease in literature or if the methods have been the reference laterally from the midline. We recommend using, as a reference, the intersection of the midline with a line tangent to the inner border of the lung (as described for inner margin ratio/outer margin ratio [dotted blue line] 4 ).…”

“…chestjournal.org used repeatedly in research and guidelines. Thus, the methods by DuComb et al 2 and Sanz-Santos et al 3 were not included in our study. Nevertheless, in our opinion, the quantitative methods that include carina-to-cancer distance, inner margin ratio, and outer margin ratio are worthwhile to be validated externally in a larger study population.…”