Cytogenetic Abnormalities in a Plasmacytoma

Cytogenetic studies from a plasmacytoma, bone marrow, and peripheral blood of a patient with myelomatosis have been described. Studies on the plasmacytoma revealed a marker chromosome in 72 per cent of the cells. Ninety-eight per cent of these contained an abnormal acrocentric marker similar to that reported by Tassoni et al.2 and approximately 50 per cent of the marker-positive cells contained an MG-like chromosome. The origin of the acrocentric marker appeared to involve a translocation from an unknown chromosome to a normal D group member, and that of the MG-like marker to involve pericentric inversion of a normal A group member. The high percentage of cells from the tumor which contained the marker chromosomes makes it likely that these markers, described in low percentage in marrow or peripheral blood by others, actually were obtained from myeloma cells.