Rationale: Primary pulmonary NK/T cell lymphoma is extremely rare, and only a few cases have reported so far. Its diagnosis is mainly dependent on open-lung biopsy.
Patient concerns: Here, we report a 44-year-old male who was initially misdiagnosed as having pneumonia according to the clinical characteristics and computed tomography (CT) findings.
Diagnosis: The first lung biopsy indicated a large number of coagulative necrotic lesions, and definite diagnosis was made after the second lung biopsy following non-response to 6-day wide spectrum antibiotic therapy. The second lung biopsy showed the tumor cells were positive for LCA, CD3ε, CD30, TIA-1, Ki67 and negative for CD20, CD56, CD1a, MPO, CK, S-100, desmin, and CD34.
Interventions: This patient refused to receive further therapy and died 1 month after confirmed diagnosis.
Outcomes: Clinically, it is difficult to differentiate pneumonia from NK/T cell lymphoma in pathology due to the presence of plenty of focal necrosis in primary pulmonary NK/T cell lymphoma.
Lessons: The diagnosis of primary pulmonary NK/T cell lymphoma should be based on lung biopsy (usually multiple lung biopsies are required), immunohistochemistry and clinical and imaging findings.