When and why to perform nodal dissection in early-stage non-small cell lung cancer?

We have read with interest the article by Zhang et al[1] focused on identification of prognostic factors between T1aN0M0 and T1bN0M0 patients. In 2009, the seventh edition of TNM Classification of Malignant Tumors[2] has divided T1 patients in two subgroups introducing a 2-cm cut point in consideration of several studies, demonstrating that prognosis is statistically better in patients with tumor from 0 to 2 cm than from 2 to 3 cm. Authors' results are in agreement with this evidence since reported a 5-year survival rate, respectively, of 73.98 and 68.18% in T1a and T1b patients (p = 0.0135). At the same time, they analyzed prognostic factors for each stage I subgroups and surprisingly found that removal of six or more lymph node stations and removal of lymph node station 7 were independent favorable prognostic factors in T1bN0M0 but not in T1aN0M0. This result complies only in part with the tendency to perform extensive lymphadenectomy even in N0 cases.[3][4] In fact, the authors demonstrated that when tumor size is less than 2 cm, the number of lymph node stations removed is not associated with any survival improvement. Their conclusion is that nodal dissection should be proposed in T1bN0M0 patients with therapeutic intent, whereas nodal sampling should be performed in T1aN0M0 to confirm preoperative stage. Some considerations need to be done. They are as follows: First, the explanation of nodal removal utility in stage I disease is uncertain. One hypothesis is that having more nodes dissected increases the staging accuracy, upstaging patients who would have otherwise been included in N0 group. This hypothesis denies therapeutic role of lymph nodes removal. Second, the authors report that overall survival was obtained considering only patients died of recurrent disease. However, they did not report the time interval between surgery and relapses. Moreover, they did not report where relapses presented (lymph nodes, ipsilateral parenchyma, and contralateral parenchyma). We think that it should be very interesting to investigate any relationship between extension of lymphadenectomy and different patterns of recurrences presentation. This information could be useful to understand the effective role of nodes removal and its explanation. Third, we underline that when nodal sampling is recommended, as in T1aN0M0 patients, at least six nodes should be always removed according to the seventh TNM edition about minimum number of lymph nodes needed for histological examination.[2] Finally, we underline the role of positron emission tomography/computed tomography scan in preoperative staging to predict prognosis and determine surgical strategy, also for nodal management, based on tumor metabolic activity. Tsutani et al in a recent article identified tumor size less than 0.8 cm or SUVmax less than 1.5 as predictive criteria of pN0, helpful for avoiding systematic lymphadenectomy for clinical stage IA lung adenocarcinoma, even in T1b tumors.[5] In conclusion, we appreciate authors' article because it focuses the attention on a less invasive surgical approach in case of early-stage non-small cell lung cancer.