As the world turns, evolving lymphoma classifications-past, present and future.

The last century and a half has seen first the recognition of lymphomas, and then the publication of one lymphoma classification after another often together with highly critical comments about preceding classifications or a welcome that was less than warm. The introduction of HUMAN PATHOLOGY in 1970 came just before one of the very acrimonious periods in lymphoma classification, as we were learning more about the normal immune system and with the proposed functional lymphoma classifications of Lukes/Collins and Kiel in 1974 relating the lymphomas to their normal B-cell or T-cell 'counterparts'. Those difficult times were followed by the regressive strictly morphologic NCI Working Formulation in 1982, with the REAL classification in 1994 putting us back on a rational path, once again grouping the lymphoid neoplasms first into those of B-cell and T- and putative NK-cell origin, and then using multiple parameters to define specific entities. Planning for the first modern WHO lymphoma classification began soon afterward, with concordance and collegiality leading to the 2001 WHO classification, which then evolved with publication of the 2008 and 2016 WHO classifications. While this review looks at these important past developments which have gotten us to where we are today, it also concentrates on where we are now, what has been learned since the most recent WHO classification and 'Blue Book' were published and on some of the unanswered questions that remain as we look to the future.