Bone marrow aspirate from a patient with carcinoma metastatic to the bone marrow, illustrating the presence of a large clump of tumor cells (arrow), surrounded by normal marrow elements. Note that the cellular outlines within the clump of tumor cells are indistinct. This is not a characteristic of any group of cells normally seen in the bone marrow.
Courtesy of David S Rosenthal, MD and Anna J Mitus, MD.