Secretory-component-producing lung cancer with hypergammaglobulinemia of secretory IgA

Studies were made on a case of well-differentiated adenocarcinoma of the lung in which the serum levels of secretory IgA (sIgA) were very high. Immunofluorescent studies showed that secretory component (SC) was found to be diffusely distributed in cancer cells. The SC was detected in the supernatant of homogenates of cancer tissues from the primary site and lymph node with metastases. The SC extracted from cancer tissue and purified colostral SC were antigenically identical. The authors conclude that the adenocarcinoma cells produced SC and secreted it into the bloodstream and that the binding of SC with polymeric IgA resulted in the hypergammaglobulinemia of sIgA. This appears to be the first reported case of SC-producing lung cancer. The authors' findings suggest that the high serum levels of sIgA in cancer patients may be due to the production and secretion of SC by tumor cells themselves rather than the reabsorption of intraluminal sIgA into the circulation through a damaged epithelium.