Background and Rationale Mantle cell lymphoma (MCL) is a rare subtype of lymphoma, accounting for about 3-6% of all non-Hodgkin's lymphoma. It is clinically prevalent in the elderly and men, commonly with gastrointestinal tract involvement. Since about 80% of patients present with advanced stage disease at diagnosis, the prognosis is very poor. Mantle cell lymphoma is less frequent in Korean than in Western countries, accounting for about 2% of all non-Hodgkin's lymphoma cases, with very poor treatment outcome as Western countries.

In Korea, the clinical information about patients with MCL is very scarce so far and does not reflect recent treatment patterns. Firstly, the incidence in Korea is relatively lower than that in Western countries, with only about 100 patients a year. Secondly, due to substandard national health insurance regulations in Korea, it was not until recently that ibrutinib for relapsed/refractory MCL was approved for coverage by the National Health Insurance. In this context, the study was designed to investigate the efficacy and safety of ibrutinib in patients with relapsed or refractory MCL in Korea.