This study analyzes the extraskeletal spread in 57 consecutively autopsied cases of multiple myeloma. Three stages of spread were recognized: stage I in which myeloma nodules were grossly confined to the skeleton; stage II with extraskeletal spread grossly confined to adjoining paraskeletal tissues; stage III with gross spread to distant sites. Extraskeletal gross or microscopic myeloma infiltrates were present in 65% of cases in this series. In stage I, microscopic infiltrates were found in 34% of cases. In addition to the gross lesions seen in stage III, all stage II and III cases showed distant microscopic tumor infiltrates. The commonest sites of these were the spleen, liver, lymph nodes and kidneys. Patients with the longest duration of illness tended to have the most widespread extramedullary involvement. Patients dying with stage III lesions tended to have a higher proportion of poorly differentiated tumor as compared to patients with stage I and II. Because of evidence of intravascular and “linear” spread in paravertebral connective tissues and because of involvement of sites other than lymphoreticular organs, it is difficult to escape the conclusion that extraskeletal sites in myeloma represent true metastases rather than autochthonous multifocal growths.

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