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INTRODUCTION

When treating patients with non–small-cell lung cancer (NSCLC), it is important to assign an accurate clinical or pathologic stage to the disease at the time of diagnosis. This adds value to the process of selecting the most appropriate therapy for the individual patient, whether it be surgical resection, neoadjuvant chemotherapy or radiotherapy, or definitive chemoradiation. The current cancer staging convention uses the basic descriptors originally proposed by Denoix1: primary tumor (T), lymph node involvement (N), and tumor metastasis (M). The contemporary classification system was adopted worldwide in 1997, after features of the 1986 combined American Joint Committee on Cancer and International Union Against Cancer TNM staging system2 were reconciled with the 1983 American Thoracic Society statement on cancer staging. The organization responsible for updating this system is the International Association for Lung Cancer Staging, which revised the staging system in 2017.3 The value of classifying NSCLC patients according to a uniform staging system that has prognostic implications based on stage grouping is difficult to overstate.

Clinical staging can be determined by CT scanning, magnetic resonance imaging (MRI), and CT/PET scanning. Pathologic staging requires biopsy, which can be obtained from cervical or anterior mediastinoscopy, during video-assisted thoracic surgery (VATS) approaches, less commonly by means of open thoracotomy, and more recently by fine-needle aspiration performed during endoscopic or endobronchial ultrasound sampling.4,5 The former endoscopic technique has now allowed for core needle biopsy in addition to fine-needle aspiration to increase histologic yield.6 Lymph node involvement has important implications for surgical treatment strategies for lung cancer.79 Patients without lymph node involvement (N0) or those with limited involvement (N1), which is usually determined at the time of surgery, are candidates for resection based on T and M status. Most patients with contralateral or supraclavicular disease (N3) or T4 involvement are not resectable (stage IIIB/C). The usual approach in stage IIIA patients with ipsilateral mediastinal nodal involvement (N2) involves either neoadjuvant chemotherapy or chemoradiation, followed by resection if appropriate, when N2 status is determined prior to resection. In some cases, surgically detected N2 disease can be discovered at the time of resection by means of lymph node dissection in conjunction with the pulmonary resection.10 There is no doubt that sampling of lymph nodes in some fashion is useful for staging and prognostic purposes. The American College of Surgeons Committee on Cancer espouses that 10 regional lymph nodes be sampled as a quality care measure. However, the extent of lymph node dissection is controversial, and the benefits of selective sampling versus complete mediastinal lymph node dissection or extended lymph node dissection are still under review.1114 A recent review article by Han and Chen15 summarizes lobe-specific drainage patterns and outlines strategies for selective nodal sampling versus systematic lymph node dissection.

LYMPH NODE MAPPING

To unify the two most widely used systems of lymph node ...

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