In situ follicular lymphoma with a 14;18 translocation diagnosed by a multimodal approach.

The main differential diagnosis for follicular lymphoma (FL, or in situ localization of follicular lymphoma) is follicular hyperplasia. However, this differentiation is quite challenging when the initial presentation of FL is in one lymph node and such a lymph node is only partially involved. In other words, only a few lymphomatous follicles are present in an otherwise nodal reactive follicular hyperplasia. The use of FISH on formalin-fixed, paraffin-embedded tissue as an adjunct to routine histomorphological and immunohistochemical evaluation is valuable for reaching an initial diagnosis of in situ follicular lymphoma in a lymph node which shows predominantly reactive follicular hyperplasia. In this report, we describe our experience in rendering such an initial diagnosis of in situ FL in an apparently healthy individual who has a single persistently enlarged lymph node. The recognition of in situ FL is of utmost importance because it is associated with localized early stage disease (stage I), which according to standard regimens is amenable to local radiation therapy with a good chance for inducing remission. To the best of our knowledge, this is the first such case reported in the English literature using innovative FISH technology on formalin-fixed, paraffin-embedded tissue in conjunction with other routine histological modalities to produce an initial diagnosis of in situ follicular lymphoma.