Diagnosis of primary cutaneous B-cell lymphoma by immunohistochemical and in situ hybridization methods

A diagnosis of primary cutaneous B-cell lymphoma is mainly supported by identification of a monoclonal B-cell population in the skin. This identification is made either by immunohistochemistry techniques using monoclonal antibodies towards the lambda or kappa chains, or by PCR for the heavy chain of immunoglobulins. Immunohistochemistry has a low sensitivity in detecting monoclonality, whereas the PCR technique is sensitive, but does not permit the localization of tumour cells in the skin. The aim of this study was to determine whether a monoclonal population in the skin could be detected by in situ hybridization. Thirty-eight skin biopsies from patients with primary cutaneous B-cell lymphoma were studied. Monoclonality was observed in 24/38 (63%) biopsies using immunohistochemical methods and 32/38 (84%) when combining this with in situ hybridization. It is concluded that kappa or lambda chain in situ hybridization is an interesting complementary technique to detect monoclonal B cells, if the immunohistochemical technique is negative.