Observations On Eosinophil Ifiltrates in The Bone Marrow Of Patients With Multiple Myeloma. Clinicopathological Correlates

Mouse eosinophils have been shown in 2011 to be required for the maintenance of long lasting plasma cells in the bone marrow and in maintaining the bone marrow plasma cell microenvironment. Human eosinophils have been shown by Wong et al to support multiple myeloma cell proliferation via a mechanism independent of IL6.

We looked at bone marrow biopsies taken from patients who had a paraprotein and in whom a diagnosis of multiple myeloma was suspected. These samples were taken solely for the purposes of diagnosisng multiple myeloma and were retrospectively reviewed from the point of view of degree of eosinophil infiltration and its correlation with tumour load, bone lytic lesions, plasma cell morphology, whether blastic, crystalline inclusions, Mott cells, flame cells and or lymphoplasmacytoid. There were no cases of IGD or E myeloma or osteosclerotic myeloma.Nonsecretory myeloma and cases of light chain myeloma with or without amyloid were included in the series. Biopsies were not performed from osteolytic lesion unless biopsy was necessary to make a diagnosis of myeloma. Myeloma was diagnosed when plasma cell infiltrate was greater than 10% on bone marrow aspirate with a paraprotein and or lytic lesions. Eosinophil infiltration did not correlate with any of the tumour clinicopathological markers but showed an inverse correlation with degree of plasmacytosis. Eosinophils were hardly ever found in marrow aspirates that had over 70% plasma cells. They were usually found in trephine sections of bone marrow in areas where there was Grade I/II fibrosis and were often found in close proximity to focal areas of plasma cell infiltration. Whether eosinophils play a role in preventing or maintaining malignant plasma cell recurrence is currently being studied.