RESUMEN
BACKGROUND: The diagnosis of Osteosarcoma (OSA) is not always straightforward. OSA may resemble Other Primary Bone Tumours (OPBT). The diagnosis of osteosarcoma is sometimes difficult especially in a very small specimen. Immunohistochemistry is one of ancillary testing types that can help the diagnosis of many tumours. The aim of this study was to evaluate the validity of Osteocalcin (OCN) and Alkaline Phosphatase (ALP) immunohistochemistry in discriminating OSA from OPBT. METHOD: This study included 50 selected human primary bone tumours, 25 cases of OSA and 25 cases of OPBT. Immunohistochemical evaluation of OCN and ALP was done for all cases. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall accuracy were calculated. RESULT: The mean age of OSA and OPBT patients was 19.6 ± 13.6 and 40.0 ± 16.3 years, respectively. Osteocalcin was positive in 17/25 (68%) cases of OSA and 16/25 (64%) cases of OPBT (p = 0.061). Alkaline Phosphatase was positive in 24/25 (96%) cases of OSA and 5/25 (20%) cases of OPBT (p < 0.001). The sensitivity of OCN in OSA diagnosis was 68%, with specificity, PPV, NPV, and overall accuracy being 36%, 52%, 53%, and 52%, respectively. The sensitivity of ALP in OSA diagnosis was 96%, with specificity, PPV, NPV, and overall accuracy being 80%, 82.7%, 95.2%, and 88%, respectively. CONCLUSION: ALP immunohistochemistry is useful in discriminating OSA from OPBT. ALP is superior to OCN in OSA diagnosis. OCN cannot be used to differentiate between OSA and OPBT.