Brief report VH gene analysis of splenic marginal zone lymphomas reveals diversity in mutational status and initiation of somatic mutation in vivo

Tumors of the splenic marginal zone can present in spleen or blood. The maturational status of the neoplastic B cells from each site appears heterogeneous, with either unmutated or mutated variableregion heavy chain (VH) genes. To determine an influence of tissue location, we assessed matched blood and splenic tumor cells from 4 patients and found them identical. However, one patient with unmutated VH genes in blood and spleen developed a clonally related diffuse large Bcell lymphoma in the chest wall. Strikingly, this subclone had undergone significant somatic mutation, with clear intraclonal heterogeneity. To our knowledge, this is the first case of a B-cell tumor showing initiation of somatic mutation in vivo. The finding emphasizes that the tissue microenvironment can influence tumor cell behavior and possibly affect disease progression. Importantly, because several replacement mutations were located within or close to the complementaritydetermining regions (CDRs), it raises the question of a role for antigen in driving tumor growth. (Blood. 2002;100:2659-2661)