Active thymus in adult with lung cancer: preliminary results from the Adult Thymic Project

Thymus is considered a non-functional remnant in adults, but some evidence suggest that it may harbor residual activity. Lung cancer patients represent the ideal model to study thymic residual activity, as their thymus can be easily harvested during surgery. This study was designed to confirm the presence of residual thymic activity both in adult mice (step 1) and in humans (step 2). In step 1, lung cancer was induced by activating k-ras mutation in a cohort of 20 young and adult mice. After killing, thymus and lungs were analyzed. Thymus was considered active when medullary was evident, cortico-medullary ratio was 50:50 or higher and adipose involution was present. In step 2, a cohort of 20 patients, undergoing surgery for lung cancer, had biopsy of pericardial fat pad, site of ectopic thymus. Thymus was considered present if Hassall’s bodies were detected. In mice, active thymus was detected in a high proportion of cases, without significant difference between adult and young (70% vs 44.4% respectively). Two cases without evidence of lung tumor had a fully functional thymus. In humans, ectopic thymus was detected in the pericardial fat pad in 2 cases (10.5%), confirmed by immunohistochemistry. Signs of previous thymic activity were detected in 8 additional patients. Results confirmed thymus activity in animal models and humans with lung cancer, providing the rationale for future systematic mediastinal thymic biopsy. The comprehension of interactions between thymus, lymphocytes and tumor may open a new potentially targetable perspective in lung cancer.