International Extranodal NK/T-cell Lymphoma Project

Inclusion Criteria: * Patients diagnosed with ENKTL, nasal type * Patients diagnosed between January 1, 1995 and December 31, 2014 * Patients treated with nonanthracycline-based therapy as the initial treatment after diagnosis * Nonanthracycline-based therapy includes the following treatments: * Radiotherapy including concurrent chemoradiation * Chemotherapy not including anthracycline such as doxorubicin (e.g. SMILE, VIPD) The type of salvage treatment will not be a criterion for exclusion. Thus, patients who had received various kinds of salvage treatment including anthracycline-containing regimens can be included. Patients who had undergone autologous or allogeneic stem cell transplantation can also be included in the analysis if they satisfy the above-mentioned inclusion criteria. Exclusion Criteria: * Patients who had received anthracycline-based therapy, such as CHOP or CHOP-like regimens, as the initial treatment. * Patients who do not have pathology slides available for central review.