The basic condition of cancer is invasion. Cancers may either express their invasive behavior initially or progress into malignancy from preexisting benign tumors, premalignant conditions, or neoplasias in situ. Invasion may compromise the function of any organ (e.g., the eye) by compression, by local destruction, or by inhibition of normal function. Invasion and local extension in the head region beyond the orbit may result in the destruction of vital structures and death. Invasion, dissemination, and metastasis may also develop early in the process of the disease when the tumor is relatively small and has not been detected.2
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