How is the growth of benign tumors suppressed?
The primary difference between a benign tumor and a malignant tumor is that the former cannot metastasize; therefore they remain within the tissue boundaries.They grow slowly and are are not very de-differentiated thereby retaining some of the tissue organization.

Another point to be considered is that benign tumors do not cause vascularization (formation of blood vessels in the tumor tissue; triggered by secretion of VEGF), which also limits its growth.