**Background:** Lung cancer is the leading cause of cancer death worldwide, with NSCLC accounting for approximately 85% of cases. Accurate preoperative TNM staging is challenging, particularly for assessing lymph node and pleural metastases. B vitamins, including vitamin B6, play roles in tissue metabolism, cellular stress responses, signal transduction, and gene expression, but their relationship with lung cancer development and progression remains inconclusive—with studies reporting tumor-promoting, tumor-suppressing, or null effects. This study aimed to investigate the association between serum B vitamin levels and intrapulmonary lymph node and localized pleural metastases in NSCLC patients.
**Methods:** This retrospective study enrolled 1,498 patients who underwent lung surgery for suspected NSCLC at Chinese PLA General Hospital from January 2016 to December 2018. Inclusion criteria included age ≥18 years, no preoperative chemotherapy/radiotherapy/targeted therapy/immunotherapy, serum B vitamin testing within three days before surgery, standardized dietary intake (approximately 2 mg/day vitamin B6 meeting Chinese DRI), and no nutritional support or supplements in the past year. Exclusion criteria included nutritional risk, uncontrolled diabetes, autoimmune disease, extrapulmonary malignancy, severe renal/hepatic insufficiency, pregnancy, and use of medications affecting vitamin B metabolism. Serum levels of vitamins B1, B2, B6 (as PLP), B9, and B12 were measured using an electrochemiluminescence method (LK3000V analyzer). Intrapulmonary metastases were pathologically confirmed per WHO Classification of Thoracic Tumors 2021 and the 8th edition of pTNM staging. Univariate and multivariate logistic regression analyses were performed, with patients divided into quartiles by serum vitamin B6 levels. Stratified analyses examined associations across age, sex, BMI, family history, smoking, alcohol consumption, and tumor characteristics.
**Key Results:** Of 1,498 patients, 1,283 had pathologically confirmed NSCLC and 215 had benign nodules. NSCLC patients had higher serum vitamin B6 levels than benign nodule patients (35.6 nmol/L vs. 32.4 nmol/L, p=0.023). Among NSCLC patients, 276 (21.5%) had intrapulmonary metastases: 223 (80.8%) with lymph node metastases and 53 (19.2%) with localized pleural metastases. The metastatic group had higher vitamin B6 levels than the non-metastatic group (36.7 nmol/L vs. 35.1 nmol/L, p=0.037) and lower vitamin B12 levels (p=0.039). In multivariate logistic regression, only vitamin B6 showed a significant positive association with intrapulmonary metastases (OR: 1.016; 95% CI: 1.002–1.031; p=0.021). Other significant factors included female sex (OR: 1.439; 95% CI: 1.039–1.993; p=0.028), tumor diameter (OR: 1.495; 95% CI: 1.337–1.672; p<0.001), multiple tumors (OR: 26.004; 95% CI: 14.517–46.580; p<0.001), and subsolid tumor as a protective factor (OR: 0.220; 95% CI: 0.142–0.342; p<0.001). Compared to the lowest quartile (Q1), the highest quartile (Q4) of serum vitamin B6 was associated with a 67.6% higher risk of metastasis (OR=1.676, 95% CI=1.092–2.574, p=0.018; p for trend=0.030). Stratified analysis revealed stronger associations in women (Q4 vs. Q1: OR=1.968, 95% CI=1.144–3.386, p=0.014; p for trend=0.014), patients with family history of cancer (Q4 vs. Q1: OR=5.337, 95% CI=1.492–19.093, p=0.010; p for trend=0.010), current smokers (Q4 vs. Q1: OR=2.462, 95% CI=1.104–5.491, p=0.028; p for trend=0.016), current drinkers (Q4 vs. Q1: OR=2.163, 95% CI=1.041–4.492, p=0.039; p for trend=0.006), patients with squamous cell carcinoma (Q4 vs. Q1: OR=3.933, 95% CI=1.421–10.888, p=0.008; p for trend=0.024), tumors 1–3 cm (Q4 vs. Q1: OR=2.152, 95% CI=1.233–3.755, p=0.007; p for trend=0.009), and solitary tumors (Q4 vs. Q1: OR=1.664, 95% CI=1.051–2.636, p=0.030; p for trend=0.043). Significant interactions were found for age, sex, smoking history, alcohol consumption, and tumor pathology, diameter, number, and density.
**Clinical Implications:** This study suggests a positive association between serum vitamin B6 levels and intrapulmonary lymph node and/or localized pleural metastases in NSCLC patients, with stronger effects in specific subgroups. The authors note that 53 patients (4.1%) had postoperative confirmation of localized pleural metastases, suggesting surgical treatment may not have been optimal for them. Preoperative vitamin B6 testing might have potential value in improving preoperative TNM staging, particularly for identifying patients who may not benefit from surgery. However, the authors emphasize that vitamin B6 does not qualify as a useful clinical biomarker due to weak associations and wide confidence intervals. The study's limitations include its retrospective design, limited sample size, inability to establish causality, and insufficiently detailed nutrition-related clinical information. Prospective studies with larger sample sizes are needed to validate these findings and explore the mechanistic relationship between vitamin B6 and lung cancer metastasis.