According to the 8th edition of the TNM classification for NSCLC, the T classifications of the tumors ≤ 3 in diameters are based only on the size of the solid component on CT or the size of the invasive component at the pathologic examination, as the size of the solid/invasive component is considered to determine the prognosis . In the present study, we first compared OS and DFS of all cases according to the clinical T factor of the TNM 8th edition in clinical stage 0 or IA lung adenocarcinoma. These results indicated that the prognosis of all cases was well stratified according to the classification in this study. However, on comparing the DFS values for cT1mi and cT1c, the 5-year DFS rate was about 25% different, despite being the same clinical IA stage; therefore, the current treatment strategy, such as the timing of treatment and surgical procedure should be considered carefully. In addition, although this stratification using the classification is useful with regard to the prognosis as well, several issues must be addressed due to switching from the conventional evaluation method involving the maximum tumor diameter. One problems is that the suitability of current treatment strategies, such as limited resection, adjuvant therapy and follow-up, is considered based on the previous staging system.
Although lobectomy is the standard procedure for managing early stage NSCLC , sublobar resection, such as segmentectomy and wedge resection, are widely performed for small NSCLC in clinical practice [9, 10]. Thus, randomized phase III studies such as Cancer and Leukemia Group B (CALBG) 140503 and Japan Clinical Oncology Group (JCOG) 0802 were conducted in United States and Japan to evaluate the non-inferiority of segmentectomy compared with lobectomy in patients with small peripheral NSCLC. The CALBG and JCOG studies targeted NSCLC patients with a whole tumor size of ≤ 2cm [11, 12]. Therefore, the whole tumor size, including ground-glass and lepidic components on radiology and pathology is required in order to evaluate separately from new TNM classification.
It is also necessary to consider surgical procedures according to the current staging system; therefore, we evaluated the optimal surgical procedures for clinical stage 0and IA adenocarcinoma according to the CT features and current T descriptors in this study. Our results showed no recurrence in cTis and cT1mi cases, regardless of surgical procedure; therefore, we may actively consider performing sublobar resection for cTis and cT1mi cases. In addition, regarding cT1a cases, only 3% of all such cases experienced recurrence (all 3 recurrent cases received lobectomy); therefore, the indication of those cases for sublobar resection is appropriate. Regarding cT1b and cT1c cases, patients who received sublobar resection experienced recurrence more often than others. Although the recurrence rate of solid tumors was significantly higher than that of part-solid tumors among cT1b cases, no significant difference was observed between part-solid and solid tumors among cT1a and cT1c cases.
Several studies have recently indicated that tumors with GGO components have a better prognosis than those without GGO component [5–7]. Fu et al. reported that the presence of GGO components was a strong predictor in patients with invasive pathological stage I NSCLC . Hattori et al. also reported that the presence of GGO component had a marked impact on the favorable prognosis of small lung adenocarcinoma . They found that solid tumors with clinical stageIA1, IA2 and IA3 had a significantly worse prognosis than the part-solid tumors of the same clinical stage . Hattori et al. also reported that segmentectomy and a larger tumor size were independent significant clinical factors of loco-regional recurrence in clinical T1aN0M0 (TNM 7th staging) solid NSCLC . There has also been a report comparing the prognosis of solid and part-solid tumors subjected to lobectomy. Takenaka et al. reported a study comparing part-solid and solid tumors among clinical stage IA NSCLC patients who received lobectomy . Although the patients with solid tumors had a significantly worse outcome than those with part-solid tumors in all cases, the propensity-matched analysis detected no significant difference in the survival between the patients with solid and part-solid tumors when matched according to the size of the solid component . These present and previous findings suggest that, for now, the indications for sublobar resection for solid tumors should be carefully determined, even in cases of small adenocarcinoma.
Several limitations associated with the present study warrant mention. First, this study had a retrospective observational design and used a single-institution Japanese database to enroll only patients who had undergone surgical resections. Second, the surgical procedures were selected according to the individual patients and were not randomized. Although the results of Phase III trials are required to establish evidence supporting limited resection for early stage NSCLC, the results of this study appeared to reflect real world data at the moment. Despite these limitations, the present study clarifies that combined evaluation with the clinical T descriptor and CT features reasonably and properly reflects the recurrence rate.