Immunohistochemistry in MM tissue sections. (A) Heterogeneous moderate and (B) homogeneous strong COX-2 expression in paravertebral-located extramedullary tumor. (B-C) Little or no COX-2 immunoreactivity in endothelial cells of small venules. (D-E) Larger clusters of plasma cells in BM samples; no significant immunoreactivity of osteoblasts and osteoclasts. (F) An example of COX-2 negativity on malignant plasma cells. This patient had massive bone marrow infiltration by malignant plasma cells that did not show COX-2 immunoreactivity. Original magnification: × 100 for panels A, B, D, E and × 200 for panels C and F. The microscope was an Axioskop (Zeiss, Germany) with Plam-Neofluar objective lens ×20, numerical aperture 10. Immersion oil was not used. The camera was a JVC model 3-CCT, and the acquisition software was Analysis Software (Softimaging Systems, Germany).