Multicenter Study on Tumor Budding in Lung Squamous Cell Carcinoma: Comparison Between Biopsy and Resection With Interobserver Variability Assessment

Grading lung squamous cell carcinoma (LUSC) is controversial and not universally accepted. The histomorphologic feature of tumor budding (TB) is an established independent prognostic factor in colorectal cancer, and its importance is growing in other solid cancers, making it a candidate for inclusion in tumor grading schemes. We aimed to compare TB between preoperative biopsies and resection specimens in pulmonary squamous cell carcinoma and assess interobserver variability. A retrospective cohort of 249 consecutive patients primarily resected with LUSC in Bern (2000-2013, n = 136) and Lausanne (2005-2020, n = 113) with available preoperative biopsies was analyzed for TB and additional histomorphologic parameters, such as spread through airspaces and desmoplasia, by 2 expert pathologists (M.M., C.N.). Results were correlated with clinicopathologic parameters and survival. In resection specimens, peritumoral budding (PTB) score was low (0-4 buds/0.785 mm²) in 47.6%, intermediate (5-9 buds/0.785 mm²) in 27.4%, and high (≥10 buds/0.785 mm²) in 25% of cases (median bud count, 5; IQR, 0-26). Both the absolute number of buds and TB score were similar when comparing tumor edge and intratumoral zone (P = .192) but significantly different from the score obtained in the biopsy (P < .001). Interobserver variability was moderate, regardless of score location (Cohen kappa, 0.59). The discrepant cases were reassessed, and consensus was reached in all cases with identification of causes of discordance. TB score was significantly associated with stage (P = .002), presence of lymph node (P = .033), and distant metastases (P = .020), without significant correlation with overall survival, tumor size, or pleural invasion. Desmoplasia was significantly associated with higher PTB (P < .001). Spread through airspaces was present in 34% and associated with lower PTB (P < .001). To conclude, despite confirming TB as a reproducible factor in LUSC, we disclose areas of scoring ambiguity. Preoperative biopsy evaluation was insufficient in establishing the final TB score of the resected tumor.