What best describes the characteristic of malignant tumors concerning cell growth?

Malignant tumors are characterized by their ability to grow and proliferate uncontrollably, often leading to invasion of surrounding tissues. When discussing substrate dependency, it refers to the requirement of cells to adhere to a surface or substrate in order to grow and survive. Malignant tumors, in contrast, frequently do not exhibit this dependence. This means they can continue to grow and divide without the need for attachment to a stable substrate, which is a fundamental trait that allows them to spread throughout the body in a process known as metastasis.

The other characteristics mentioned in the choices do not accurately reflect the nature of malignant tumors. Non-invasiveness is typical of benign tumors rather than malignant ones, which are known for their invasive growth patterns. The concept of reduced motility is also contrary to malignant tumors, which tend to be highly motile, contributing to their ability to metastasize. Lastly, contact inhibition refers to the natural process where normal cells stop dividing when they come into contact with one another. Malignant tumors often lose this property, allowing them to continue proliferating even in dense cell populations. Thus, the description that malignant tumors exhibit no substrate dependency correctly encapsulates a key trait of their aggressive and invasive behavior.