Recurrent Mantle Cell Lymphoma Isolated to the Testis After 19-Year Remission: A Case Report and Review of the Literature

• Only a handful of reports describe the rare event of primary mantle cell lymphoma (MCL) in the testis. Here, we describe the first report of MCL recurrence in the testis. • The MCL recurrence in the testis was treated successfully with orchiectomy of the affected testis followed by six doses of salvage rituximab and four cycles of high-dose methotrexate and prophylactic testicular radiation to the contralateral testis. • The MCL in our patient was characterized as cyclin D1-positive by immunohistochemistry but t(11;14)(q13;q32)-negative by fluorescence in situ hybridization (FISH). MCL with this characterization may have longer latency periods. • Aside from the classic t(11;14)(q13;q32) chromosomal translocation, known mechanisms of cyclin D1 upregulation in MCL include oncogenic mutation of the CCND1 gene, cryptic translocations of the enhancer regions of immunoglobulin light chains near the CCND1 gene, and translocations of the CCND1 gene to other loci. • The testis may provide a microenvironment that promotes cellular tumor dormancy of MCL cells, demonstrated by our patient's 19-year remission. Understanding mechanisms of clinical tumor dormancy may lead to the development of therapies that can induce life-long remission.