To investigate which, if any, of the three proteins secreted by the metastatic breast cancer cells (SLPI, TSLP, and G-CSF) have a functional role in tumor growth and metastasis, we next used lentivirally-transduced shRNA to stably inhibit translation of SLPI, TSLP, or G-CSF in 4T1 cells. The gene discussed is SLPI; the disease is breast carcinoma.