Because the monoclonal antibody MIB-1 recognizes a formalin-resistant epitope of Ki-67, it can be used in routinely fixed, paraffin-embedded tissue.Ki-67/MIB-1 immunostaining has become clinically relevant for other endocrine tumor types in situations where discrimination between benign and malignant tumors is challenging. The gene discussed is MIB1; the disease is cancer.