The probability of nodal metastasis in novel T-factor: the applicability of sublobar resection.

Background: Recently sublobar resection is often indicated for small-sized peripheral lung cancer according to size or the consolidation/tumor ratio on CT; however, the T-factor classification drastically changed in the 8th version. We investigated the relationship between a novel clinical T-factor classification, which includes other clinical information and the pathologic N-factor, to evaluate the applicability of the novel T-factor classification to sublobar resection. Methods: From January 2013 to October 2017, 545 patients with cTis or cT1 lung cancer underwent surgery. Patients with non-peripheral type, induction treatment, cN >= 1, cM1, and those without nodal dissection, preoperative evaluation by thin-sliced CT or FDG-PET were excluded. Finally, 325 patients were eligible for inclusion. All clinical parameters were prospectively collected and retrospectively analyzed. The 8th edition of TNM classification was utilized. Results: Nodal metastasis was detected in 38 (11.7%) patients. Among cTis/1mi/1a/1b/1c patients (n=10/11/51/146/107), pN1 and pN2 were observed in 0/0/2/9/ 10 and 0/0/1/8/8, respectively. cT1b/c patients showed a significantly higher rate of nodal metastasis (P=0.024). Among 253 cT1b/c patients, solid-type tumors (n=177) were more frequently associated with nodal metastasis. A ROC curve analysis revealed that SUVmax 1.9 was the cutoff value (AUC=0.827) for the presence of nodal metastasis. Using the 2 parameters of solid-type or SUVmax >= 1.9, we could successfully exclude patients with nodal metastasis, for whom sublobar resection is not indicated. Conclusions: In terms of nodal metastasis, sublobar resection can be applicable for all cTis/1mi tumors; patients with cT1a/b/c tumors with mixed GGO and low SUVmax are candidates for sublobar resection.