Secretory component in breast cancer. Analysis of the levels in primary and metastatic disease.

Levels of secretory component (SC) were measured in breast tumors from 95 patients with primary or metastatic cancer. Tumor cytosols were prepared by polytron disruption and high speed centrifugation (105,000 g X 30 min) and SC was measured using a sensitive radioimmunoassay which detects primarily free SC. In frozen samples stored for up to 5 months SC resisted degradation and could be measured quantitatively without interference. In primary tumors from patients between ages 28 and 97, SC positive samples ranged from 4 ng/mg protein to 600 ng/mg protein. In metastatic lesions, SC positive samples ranged no higher than 46 ng/mg protein. The studies indicate that SC can be measured quantitatively in both primary and metastatic tumors and that prolonged storage does not interfere with measurements of SC. The wide variation in SC levels in primary tumor samples may be related to a susceptibility to metastasis. Further, the low levels of SC in metastatic lesions could indicate a potential for SC involvement in immune regulation of tumor growth.