Extraosseous tumours of the skin were observed in three patients with multiple myeloma. Routine histopathologic study of paraffin-embedded specimens from these tumors suggested the diagnosis of lymphoma or reticulum-cell sarcoma. The cutaneous myeloma cells stained in a characteristic fashion with methyl green-pyronin and touch imprints of the tumors stained with Wright's stain demonstrated, however, typical myeloma cells.
The myeloma serum proteins from two patients were characterized as IgG-L and BJP-K, respectively. These immunoglobulins or immunoglobulin fragments were not demonstrated in the cutaneous metastases by direct fluorescent staining. Touch imprints from one tumor revealed positive cytoplasmic staining for IgM-K and IgM-L in medium-sized lymphocytes, but not in tumor cells. In cryostat-sectioned specimens from this tumor, these fluorescent cells appeared to buttress the tumor masses in the skin. The possibility that these cells may reflect a host mechanism for rejecting tumor cells is suggested.
Wuepper KD, MacKenzie MR. Cutaneous Extramedullary Plasmacytomas. Arch Dermatol. 1969;100(2):155-164. doi:10.1001/archderm.1969.01610260031005