Highly proliferative refers to a cell or tissue with a high rate of cell division or growth. In the context of cancer, highly proliferative cells are those that divide rapidly and uncontrollably, leading to the growth and spread of the tumor.

The rate of proliferation is an important factor in determining the aggressiveness of a cancer, as faster-growing tumors tend to be more difficult to treat and have a poorer prognosis. Cancer cells that are highly proliferative may be more resistant to chemotherapy and radiation therapy, as these treatments target rapidly dividing cells.

To assess the proliferative activity of cancer cells, doctors may perform tests such as Ki-67 immunohistochemistry, which measures the percentage of cancer cells that are actively dividing. This information can help guide treatment decisions and predict the likely course of the disease.