A case report and literature review of rare intracranial and extracranial dual-lesion diffuse large B-cell lymphoma with heterogeneous subtypes (GCB type + ABC type).

Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of malignant lymphoma in adults. According to the gene expression profile, it can be classified into germinal center B-cell (GCB) type and activated B-cell (ABC) type. Cases with coexistence of the two subtypes and cross-site involvement are extremely rare. Herein, we report a 65-year-old female patient who presented with blurred vision in the right eye. Imaging examinations revealed space-occupying lesions in the left thalamus, basal ganglia, deep temporal lobe and left temporal muscle. Pathological biopsy and immunohistochemistry confirmed that the intracranial lesion was ABC subtype DLBCL and the temporal muscle lesion was GCB subtype DLBCL. Fluorescence hybridization (FISH) excluded c-MYC, Bcl-2 and Bcl-6 gene rearrangements. No involvement of other sites was detected by PET-CT and bone marrow biopsy. The patient initially received 2 cycles of rituximab combined with high-dose methotrexate chemotherapy. Efficacy evaluation showed stable disease (SD) of the intracranial lesion and complete response (CR) of the temporal muscle lesion. Subsequently, the regimen was adjusted to 6 cycles of cytarabine combined with temozolomide chemotherapy followed by radiotherapy for the intracranial lesion. Eventually, the intracranial lesion achieved partial response (PR) and the temporal muscle lesion maintained sustained CR. Up to the date of follow-up, the patient's condition was stable without recurrence. Combined with literature review, this article discusses the possible mechanisms of the coexistence of dual-subtype DLBCL (clonal evolution or biclonal origin), the potential pathways of temporal muscle metastasis and the impact of subtype differences on treatment response, which provides clinical reference for the diagnosis and individualized treatment of such rare cases.