Pathology of malignant lymphomas

Although the subject is now seldom formally addressed, much of the pathologic research into malignant lymphoma is still tacitly directed at developing a rational and reproducible classification. Pure morphology, while remaining of critical importance in the diagnosis of malignant lymphomas, has been exhausted as a means of understanding the biology of these tumors, which must be the eventual basis of a firm, enduring and clinically relevant classification. Thus, histopathologists have turned first to immunohistochemistry and now to molecular genetics to make sense of their morphologic observations. Correlation of various genetic (including oncogenetic) rearrangements with morphology has preoccupied pathologists this past year and has led to important advances in the understanding of B- and T-cell lymphomas. Lymphomas occurring in a setting of immunodeficiency, whether therapeutically induced or acquired, have received special attention, and the possible role of the Epstein-Barr virus in their pathogenesis has induced pathologists to develop exciting in situ molecular hybridization techniques for its identification in tissues. The certainties underlying the diagnosis and classification of Hodgkin's disease (in which Epstein-Barr virus also appears to play a role), formally the only truly secure area for pathologists, have been disturbed, and the borderline between Hodgkin's disease and non-Hodgkin's lymphoma is now seriously blurred. The lymphoma pot has been well and truly stirred; we must now wait to see what the new sediment offers.