Microscopically, a neoplasm infiltrates the colon wall and perivisceral adipose tissue; the neoplasm is formed by cells with morphology and immunophenotype of a mature plasma cell (CD79a+, CD138+, MUM1+, CD20-, and Bcl1-) with monotypic expression of K light chains and IgA heavy chains. The gene discussed is SDC1; the disease is neoplasm.