P1.10-06 Pathological Characterization of Radon-Induced Lung Cancer in Rats

Abstract

Radon is a radioactive gas, considered the leading cause of lung cancer in non-smokers. Although the risk of lung cancer is linear, there is no safe level and even low dose can be associated with risk. In humans, no specific pathological subtypes of lung cancer have been clearly associated with radon. In animals, the French Atomic Energy Commission (CEA) exposed to low dose of radon (25 working level month, WLM) a large cohort of rats in a radon-exposure chamber, showing lung cancer induced by low exposure (Chameaud J, Radiation Prot Dosimetry 1984). We aimed to describe pathological features of radon-induced tumors in rats from the CEA’s cohort. Retrospective assessment of archival samples available of the rats exposed to low-dose radon in the Laboratoire de Pathologie Pulmonaire Experimentale, COGEMA (France), between 1989 and 1992. Autopsy reports were also reviewed. The pathological assessment was performed for a thoracic oncology pathologist (JA) in H&E staining slides according to the current WHO histological classification. Samples from 117 rats were collected. Among 104 tumors, to date the analysis has been performed in 94. Forty tumors (43%) were classified as malignant, 28 (30%) as uncertain malignant potential (UMP) and 26 (28%) benign. In 2 rats (2%) synchronous malignant and non-malignant tumors were observed. Among the malignant tumors, 23 (58%) were epithelial and 17 (42%) non-epithelial. Lung carcinoma was the most common primary epithelial tumor (n=10, 43%), followed by abdominal area tumors (n=5, 22%), and thyroid (n=3, 13%). In the UMP group, 7 (25%) were epithelial and 21 (75%) non-epithelial, with no lung tumors observed. In the benign group, most of them (n=24, 92%) were epithelial, with 4 cases with lung atypical adenomatous hyperplasia-like lesions; 2 synchronous with other malignant tumors (n=1 lymphoma, n=1 cutaneous squamous cell carcinoma). A total of 26 tumors (27%) had thoracic involvement: 4 (15%) primary lung non-malignant lesions, 11 primary lung malignancies (42%) and 11 with metastases from other tumors (42%). As primary malignant lung tumors, we observed: 7 (64%) adenocarcinoma in situ, one papillary adenocarcinoma, one undifferentiated large cell carcinoma with bilateral metastases, one metastatic squamous carcinoma and one metastatic undifferentiated tumor, compatible with sarcoma In this cohort of radon-induced tumors in rats, we observed different tumor types, from non-malignant lesions to aggressive malignancies, with predominance of epithelial tumors. Lung carcinoma was the most common primary tumor and adenocarcinoma the histological subtype more observed, with histological similarities with humans.