[MALT B cell lymphoma with kidney damage and monoclonal gammopathy: a case study and literature review].

We report a case of low-grade B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) involving the left kidney and simultaneous onset of a monoclonal gammopathy IgM kappa. No predisposing local inflammatory condition was identified. Following left nephrectomy, the renal specimen showed the centrocyte like cells and lymphoid cells in the lymphoepithelial lesions were positive for CD20 and CD79α. The neoplastic cells expressed monotypic cytoplasmic IgM kappa. The demonstration of bone marrow cells of B-lineage expressing the same monoclonal protein as the tumor suggested bone marrow involvement, even in the absence of identical morphology. Despite chemotherapy and rituximab treatment, clinical follow-up showed right kidney extension with high-grade transformation, and finally systemic dissemination. This case illustrates that the kidney is among the sites that may be involved by MALT B-cell lymphomas in a primary or secondary fashion, and the need for expanded investigation of the possible dissemination. We review the literature on this unusual extranodal lymphoma.