Aims Progressive transformation of germinal centres (PTGC) is a reactive process of undetermined aetiology. Although usually seen as nodal disease, it can occur at extra-nodal sites, such as oral cavity, gastrointestinal tract and skin. To determine if PTGC occurs in the orbit, we reviewed cases of ‘florid reactive lymphoid hyperplasia’ affecting this region.

Methods The cases were retrieved and were investigated using a panel of immunohistochemical stains and PCR clonality studies. Cases were jointly assessed by a specialist ophthalmic pathologist and a haematopathologist.

Results Eight cases were retrieved from file, and all showed morphological features that fell within the spectrum of changes seen in PTGC. A diagnosis of PTGC was made in cases with expanded germinal centres showing >90% infiltration by mantle cell lymphocytes. Cases where there were other PTGC features, but <90% infiltration by mantle lymphocytes, were classified as incomplete or focal PTGC.

Conclusions The authors observed the spectrum of changes previously described in nodal tissue, finding follicular hyperplasia, follicular lysis and PTGC in the orbit. They also identified one specimen that harboured a malignant lymphoma. The study demonstrated that lymphoid proliferations within the orbit can be difficult to evaluate. The authors recommend that such proliferations are investigated with a broad panel of immunohistochemical stains together with PCR where appropriate, and that there should be a low threshold for referral to a specialist haematopathologist.