Which of the following determines whether a tumor is classified as malignant?

A tumor is classified as malignant primarily based on its invasive growth into surrounding tissues. Malignant tumors have the ability to invade adjacent tissues and organs, disrupting their normal functions. This invasive characteristic is a hallmark of malignancy because it indicates that the tumor can spread beyond its initial site, leading to further complications, potential metastasis (spread to distant sites via the bloodstream or lymphatic system), and greater risk to the patient.

Visible vascularization, while often associated with tumor growth as tumors can stimulate the formation of new blood vessels (angiogenesis) to support their increased metabolic needs, is not a determining factor for malignancy on its own.

The size of the tumor mass can provide some information about its potential aggressiveness, but a larger tumor is not necessarily malignant, as some benign tumors can reach significant sizes without invading nearby tissues.

Cellular differentiation reflects how much the tumor cells resemble normal cells of the tissue of origin. While poorly differentiated cells in a tumor often suggest a more aggressive and potentially malignant behavior, differentiation alone cannot determine malignancy, as even well-differentiated tumors can be malignant if they invade surrounding tissues.

Therefore, the invasive growth into surrounding tissues is the crucial factor that distinguishes malignant tumors from benign ones, confirming the classification of a