Objective Primary vitreoretinal lymphoma (PVRL) is a rare type of lymphoma wherein the lesions are limited to the eyes. PVRL is difficult to diagnose because of the challenges related to obtaining sufficient samples for biopsy. Moreover, PVRL has poor outcomes and often leads to the development of central nervous system (CNS) lesions during its course. Two studies recently reported that approximately 70%‐80% of patients with vitreoretinal lymphoma have MYD88L265P, which is frequently mutated in primary CNS lymphoma (PCNSL). PCNSL is closely associated with PVRL. The mutation of CD79BY196 has been also frequently detected in PCNSL. Thus, we examined the mutation in PVRL to clarify its diagnostic and prognostic potential. Method By using direct sequencing and allele‐specific polymerase chain reaction, we examined the mutation of CD79BY196 and MYD88L265P in the DNA extracted from the vitreous fluid of 17 patients with PVRL upon diagnosis. We also retrospectively analyzed their prognostic potential for PVRL. Results Among the included patients, six patients (35%) were found with CD79BY196 mutations. Twelve (71%) patients were positive for MYD88L265P, and six samples from patients with benign uveitis were negative for both mutations. Interestingly, six patients with CD79BY196 mutations developed CNS diseases significantly earlier (16.5 months) than 11 patients with CD79BWT (67 months; P = 0.0135). Conclusion Detecting CD79BY196 in vitreous DNA may contribute to the confirmation of the diagnosis and may have a prognostic potential for patients with PVRL.

Chronic active Epstein-Barr virus infection (CAEBV) is a lymphoproliferative disorder characterized by the clonal proliferation of EBV-infected T or NK cells and is related to severe systemic inflammation. This study aims to investigate STAT3 to elucidate the mechanism underlying the CAEBV development. We determined that STAT3 was constitutively activated in EBV-positive T- or NK-cell lines. We also determined that STAT3 was activated in the peripheral blood mononuclear cells (PBMCs) containing EBV-infected clonally proliferating T or NK cells in six of seven patients with CAEBV. We conducted direct sequencing of the STAT3 Src homology 2 (SH2) domain, which has previously been reported to be mutated in T- or NK-cell neoplasms. No mutation was detected in the STAT3 SH2 domain in patients with CAEBV. Next, we investigated the effects of ruxolitinib, an inhibitor of both JAK1 and JAK2, which phosphorylates and activates STAT3. Ruxolitinib suppressed the phosphorylation of STAT3 in EBV-positive T- or NK-cell lines. Ruxolitinib also decreased the viable cell number of EBV-positive T- or NK-cell lines and PBMCs from patients with CAEBV. Furthermore, ruxolitinib suppressed the production of inflammatory cytokines in the cell lines and CAEBV patient-derived cells. In conclusion, constitutively activated STAT3, which promotes survival and cytokine production, could be a therapeutic target for CAEBV.