Factors associated with lymph node metastasis upstage after resection for patients with micropapillary lung adenocarcinoma

Background Micropapillary adenocarcinoma has a poor prognostic histological pattern. Additionally, preoperative detection of lymph node metastases by preoperative examination is difficult in some patients with micropapillary adenocarcinoma, and postoperative upstage may occur. However, clinicopathological features of patients with micropapillary adenocarcinoma with nodal upstage have not been established, therefore this study aimed to identify the factors associated with potential lymph node metastases during preoperative examination to ensure effective surgical procedures. Methods Between January 2011 and December 2020, 1029 patients received complete resection for primary non‐small‐cell lung cancer by lobectomy or more extensive resection with systematic lymph node dissection at this institution. One hundred and thirty‐one patients diagnosed with adenocarcinoma with micropapillary component were included in this study. The clinicopathological features of patients with nodal upstage whose postoperative N stage was more advanced than the preoperative N stage were examined. Results Forty patients had nodal upstage after resection. 18F‐fluorodeoxyglucose (FDG) positron emission tomography‐computed tomography (PET‐CT) revealed that a maximum standardized uptake value (SUVmax) ≥5 for the primary lesion was significantly associated with postoperative nodal upstage. There were no significant differences in terms of sex, age, smoking history, surgical procedure, and diabetes. Among 38 patients with nodal upstage, 23 patients had no significant preoperative lymphadenopathy and showed no abnormal FDG uptake in the lymph nodes on 18F‐FDG‐PET‐CT, respectively. Conclusions Lymph node metastases were suspected in patients preoperatively diagnosed with micropapillary adenocarcinoma with FDG SUVmax ≥5 for the primary tumor. Therefore, standard surgical resection and careful lymph node dissection should be performed for such patients. SUVmax ≥5 uptake in the primary tumor was significantly more frequent in the nodal upstage group than in the no nodal upstage group. There were no significant differences between the groups in terms of sex or age at surgery, clinical stage, diabetes, tumor location, and presence or absence of obstructive ventilatory impairment.