Lymphoma Ki67, also known as the proliferation index, is one of the indicators in immunohistochemistry performed after the pathological diagnosis of lymphoma. If this proliferation index is higher, it indicates that the activity of the tumor is stronger, and its proliferation is more active, thus the tumor should be given sufficient attention. Of course, active treatment should be pursued. Therefore, Ki67 reflects the activity of a tumor; if the index is very high, greater than 90%, it sometimes implies that the tumor can grow very rapidly, or not only grows significantly but might also spread to many places.