Local invasion

Local invasion
Most benign tumors grow as a cohesive expansible masses that develop a rim of condensed connective tissue or capsule at the periphery and they don t penetrate that capsule or the surrounding normal tissues.
The line of cleavage between the capsule and surrounding normal tissue facilitates surgical removal of benign tumors.
On the other hand; malignant tumors are invasive and infiltrative destroying normal surrounding tissues. They usually lack a well defined capsule or line of cleavage; so tumor s enucleation is impossible and it s surgical removal require excision of a considerable margin of healthy apparently un involved tissue.

Metastasis
This process involves invasion of blood vessels, lymphatics and body cavities by malignant tumor, followed by transport and growth of secondary tumor masses that are disconnected from primary tumor. This is a pathognomonic criteria of malignancy as almost all malignant tumors are capable of metastasis except basal cell carcinoma of skin and brain tumors.