Radiologic findings to predict low-grade malignant tumour among clinical T1bN0 lung adenocarcinomas: lessons from histological subtypes

Abstract

Objective: Some clinical T1bN0 (cT1bN0) lung adenocarcinomas (2-3 cm) are thought to have less-aggressive and less-malignant behaviour although most cT1aN0 tumours (≤2 cm) are indolent. The present study aimed to identify pre-operative radiographic findings that can predict cT1bN0 lung adenocarcinoma with low-malignant aggressiveness in consideration of histological subtypes.

Methods: The clinicopathological features and prognoses of 224 consecutive patients (histological subtype set, n = 122; prognosis set, n = 224) with cT1bN0 lung adenocarcinoma were retrospectively examined. Adenocarcinoma in situ, minimally invasive adenocarcinoma, lepidic, node-negative papillary and node-negative acinar predominant invasive adenocarcinomas were defined as low-grade malignant, whereas solid, micropapillary, node-positive acinar and node-positive papillary predominant invasive adenocarcinoma were defined as high-grade malignant.

Results: Receiver operating characteristics analysis revealed that the criteria of solid tumour size ≤1.8 cm on high-resolution computed tomography and the maximum standardized uptake value ≤3.2 on positron emission tomography/computed tomography could predict low-grade malignant tumour in the histological subtype set. Among 95 (42.4%) of 224 patients who met the criteria for the prognosis set, 94 (98.9%) had no lymph node metastasis and 93 (97.9%) had no recurrence (median follow-up, 43.6 months). The 3 year recurrence-free survival rates were 94.9 and 79.0% in patients whose pre-operative findings met and did not meet the criteria, respectively.

Conclusions: Pre-operative radiographic findings of solid tumour size and the maximum standardized uptake value could identify low-grade malignant tumour among cT1bN0 lung adenocarcinomas, which account for about half of all cT1bN0 tumours. Patients with pre-operative lung tumour findings that fulfill the criteria could be candidates for sublobar resection.

Keywords: SUVmax; lung adenocarcinoma; solid tumour size; sublobar resection; subtypes.