THE VALUE OF IMMUNOHISTOCHEMISTRY
IN THE ASSESSMENT OF BONE MARROW DISORDERS

Attilio Orazi, M.D., FRCPath. and Dennis P. O'Malley, M.D.

MALIGNANT LYMPHOMAS Numerous B-cell and T-cell antigens are able to survive fixation and acid decalcification and can be used to confirm the presence of lymphomatous involvement in routinely processed bone marrow biopsy material. Although immunophenotyping of lymphoid malignancies in bone marrow sections can be successfully accomplished, it is always preferable to subtype lymphomas using material from the original involved lymph node or other primarily affected organ. Bone marrow should, however, be used to subtype cases of lymphoproliferative disorders which are associated with typical diagnostic findings in this organ (e.g. hairy cell leukemia), or in the rare cases of primary bone lymphomas. In most cases all that the hematopathologist needs to determine is whether the lymphomatous proliferation in the bone marrow is morphologically compatible with the subtype of lymphoma which is known to affect the patient. In this context, immunohistochemistry can be very helpful by allowing an objective comparison of the immunophenotype of the malignant cells in the primary affected organ and in the marrow. This is especially important in cases in which morphology shows discordant cytologic features (e.g. large cell transformation of B-CLL/SLL). A word of caution: most antibodies reactive with lymphoid antigens in bone marrow sections are not totally specific. A panel approach based on the use of selected lineage-specific antibodies is mandatory in the assignation of immunophenotype. The antibodies used in our practice and their reactivities will be discussed within the framework of the lymphoma subtypes as categorized by the REAL/WHO classifications.