Proposal of a grading system for squamous cell carcinoma of the lung - the prognostic importance of tumour budding, single cell invasion, and nuclear diameter

Abstract

The prognostic markers of lung squamous cell carcinoma (LSCC) are less investigated. The aim of our study was to evaluate tumour budding (TB), minimal cell nest size, nuclear diameter (ND), and spread through air spaces (STAS) among patients with resected LSCC, semi-quantitatively. Furthermore, we aimed to identify a grading system for the best prognostic stratification of LSCC. Patients who underwent surgical resection at the Department of Surgery, University of Szeged between 2010 and 2016 were included. Follow-up data were collected from medical charts. Morphological characteristics were recorded from histologic revision of slides. Kaplan-Meier analysis, log rank test and Cox proportional-hazards model, ROC curve analysis, and intraclass correlation were utilised. Altogether 220 patients were included. In univariate analysis, higher degree of TB, infiltrative tumour border, larger ND, the presence of single cell invasion (SCI) and STAS were associated with adverse prognosis. Based on our results, we proposed an easily applicable grading scheme focusing on TB, ND, and SCI. In multivariate analysis, the proposed grading system (p_OS < 0.001, p_RFS < 0.001) and STAS (p_OS = 0.008, p_RFS < 0.001) were independent prognosticators. Compared to the previously introduced grading systems, ROC curve analysis revealed that the proposed grade had the highest AUC values (AUC_OS: 0.83, AUC_RFS: 0.78). Each category of the proposed grading system has good (ICC: 0.79-0.88) reproducibility. We validated the prognostic impact of TB, SCI, ND, and STAS in LSCC. We recommend a reproducible grading system combining TB, SCI, and ND for proper prognostic stratification of LSCC patients. Further research is required for validation of this grading scheme.

Keywords: Grade; Lung squamous cell carcinoma; Nuclear diameter; Single-cell invasion; Spread through air spaces; Tumour budding.

Fig. 1

Examples of relevant histologic parameters and their levels. a Lack of tumour budding (HE, 100×). b Intermediate level of tumour budding (buds – arrows, HE, 400×). c High level of tumour budding (buds – arrows, HE, 400×). d Squamous cell carcinoma with small nuclear diameter (≤ 4 lymphocytes – arrow, HE, 400×). e Squamous cell carcinoma with large nuclear diameter (> 4 lymphocytes – arrow, HE, 400×). f Spread through air paces (STAS) in a case of squamous cell carcinoma (STAS – arrows, HE, 100×)

Fig. 2

Kaplan-Meier curves for OS and RFS according to different grading systems. a, b Regarding the grade defined by Kadota et al, significant differences were demonstrated among OS and RFS estimates of G1 vs.G3 (p_OS < 0.001; p_RFS < 0.001) and G2 vs G3 p_OS < 0.001; p_RFS<0.001), but not between G1 vs. G2 (p_OS = 0.131; p_RFS = 0.128). c, d Concerning the grade introduced by Weichert et al., significant differences were found among OS and RFS estimates of G1 vs. G2 (p_OS = 0.006; p_RFS = 0.010) and G1 vs. G3 (p_OS < 0.001, p_RFS = 0.004), but not between G2 vs. G3 (p_OS = 0.066; p_RFS = 0.275). e, f Regarding the proposed grade combining tumour budding, nuclear diameter and single cell invasion, the Kaplan-Meier estimation revealed significant differences among OS and RFS estimates of all grades (G1 vs. G2: p_OS = 0.035; p_RFS < 0.001; G1 vs. G3 p_OS < 0.001; p_RFS < 0.001; G2 vs. G3 p_OS = 0.003; p_RFS = 0.014)