The development of malignant lymphoma in myoepithelial sialadenitis with and without Sjögren's syndrome was investigated. At first, prelymphomatous proliferation areas showing a polytypic immunoglobulin (Ig) pattern were seen. These transformed into malignant lymphoma with a monotypic Ig pattern, at first in small, circumscribed proliferation areas ("early lymphoma") and later in large, conflue...