What is the radiological definition of part-solid tumour in lung cancer?†

The method of evaluating ground glass opacity (GGO) on thin-section computed tomographic (CT) scans is an issue of debate in early lung cancer. The term 'part-solid tumour' is frequently misused, and there is no consensus for its definition.

A retrospective study was conducted on 775 consecutive patients with resected lung adenocarcinoma of clinical stage IA between 2008 and 2013. Part-solid tumours (PSTs) having a ground glass component and consolidation were divided into two categories using the radiological criterion of a consolidation-to-tumour (C/T) ratio of 0.5. Lung cancers were classified into four groups: (i) pure ground glass nodule (pGGN) (C/T ratio = 0); (ii) ground glass-predominant PST (GP-PST) (0< C/T ratio < 0.5); (iii) consolidation-predominant PST (CP-PST) (0.5 ≤ C/T ratio < 1) and (iv) solid tumour (ST) (C/T ratio = 1). We investigated the clinicopathological features and prognoses of patients with GP-PST and CP-PST.

The incidence of lymphatic invasion was 0% in pGGN, 0.8% in GP-PST, 16.8% in CP-PST and 46.2% in ST ( P  < 0.001). Among the PST lung cancers, predictors for lymphatic invasion were C/T ratio (OR 20.631, 2.755-154.508, P  = 0.003) and tumour size (OR 3.228, 1.413-7.375, P  = 0.005) in a multivariable analysis. The difference in recurrence-free survival between GP-PST and CP-PST was statistically significant [98.9 vs. 91.3% (5 years), P -value = 0.044].

PST comprised two categories in terms of invasiveness and prognosis based on the radiological criteria of a C/T ratio of 0.5. Ground glass-predominant PST and consolidation-predominant PST should be distinguished, and strategies specific to each determined using these terminologies.