Abstract
CART therapy is an approved therapy in advanced ALL. The mechanism of relapse post-CART therapy is under vigorous research. We report a 9-year-old boy who received CD19-CART therapy after BM ALL relapse post-HSCT. He presented with unilateral eye swelling which was initially managed as orbital cellulitis. Later on, it was proven to be an isolated ALL orbital relapse without peripheral blood B-cell detection or BM involvement. Despite radiotherapy, he subsequently developed refractory CD19 positive ALL BM relapse. This case highlights the possibility of unusual relapse sites after CART-therapy and that regular peripheral B-cell monitoring is not enough to assure remission status. Better monitoring tools are needed to detect early disease relapse. Further understanding of the pathophysiology of isolated extramedullary relapse post-CART therapy is warranted to improve the management of such challenging presentations.