CCND1 and hairy cell leukemia: The expression of cyclin D1 is the most important characteristic with regard to immunophenotyping; in fact, in our series, all the patients displayed an overexpression of cyclin D1, but one must not forget that it can also occasionally be positive in hairy cell leukaemias, in 16% of myelomas, and very occasionally in some large B-cell lymphomas.