A case report of T cell/histiocyte-rich large B cell lymphoma misdiagnosed as lymphomatoid papulosis.

Rationale: T cell/histiocyte-rich large B cell lymphoma (THRLBCL) is an uncommon B cell lymphoma characterized by < 10% large neoplastic B cells in a background of abundant T cells and frequent histiocytes. If a skin lesion is the first clinical sign of lymphoma, the diagnosis might be difficult and misdiagnosed.

Patient Concerns: A 60-year-old woman presented with multiple erythematous umbilicated nodules on her left upper back for 3 months.

Diagnoses: Through punch biopsy of the back lesion and additional excisional right inguinal lymph node biopsy, the patient was diagnosed with cutaneous metastasis of THRLBCL.

Interventions: The patient was referred to the Hemato-oncology Department for chemotherapy.

Outcomes: R-CHOP chemotherapy is currently in progress, and some skin lesions show improvement.

Lessons: Skin lesions might be the first clinical sign of THRLBCL and when THRLBCL is suspected, careful further evaluation is essential for accurate diagnosis and treatment.