p21 was positive in bony callus and sarcoidosis in up to 30% of GCs, in up to 70% of GCs in tuberculosis, and the mandibular brown tumour, and in more than 70% of the GCs of foreign body granuloma, fibroid epulis and the brown tumour of the femur. The gene discussed is CDKN1A; the disease is sarcoidosis.