Prognostic significance of immunohistochemical expression of ezrin in non-metastatic high-grade osteosarcoma. Ezrin is a membrane-cytoskeleton linker protein involved in regulating growth and metastatic behaviour of cancer cells. The study evaluated ezrin expression and its prognostic value in patients with non-metastatic osteosarcoma.Ezrin expression and pattern of staining (cytoplasmic or membraneous and cytoplasmic) were assessed using immunohistochemistry on slides from tumour biopsy. We studied 95 patients (median 16 years, range: 4-39 years) with primary non-metastatic osteosarcoma of the extremity treated by neoadjuvant chemotherapy based on methotrexate, cisplatin, doxorubicin and ifosfamide.Seventy-six patients (80%) showed ezrin immunoreactivity: in cytoplasm (37, 47%) and in cytoplasm and membrane (42, 53%) of tumour cells. Immunohistochemical staining score was: 1+ (16, 24%), 2+ (10, 13%), 3+ (17, 21.5%) and 4+ (36, 45.5%). Ezrin and score expression were not related to gender, site, alkaline phosphatase (AP), LDH serum levels, chemotherapy-induced tumour necrosis or patient outcome. A significant association was seen between expression pattern and prognosis. The 3-year probability of disease-free survival was 80% for patients with only cytoplasmic immunostaining and 54% for patients with cytoplasmic and membranous immunostaining (P < 0.02).Ezrin immunoreactivity can be detected in the majority of patients with non-metastatic osteosarcoma of the extremity. The pattern of ezrin staining can identify patients with different risks of relapse. In patients who only have ezrin cytoplasmic expression, a probability of EFS >80% at 5 years can be expected. These results suggest further investigations to define the relation between expression pattern, ezrin functional status and outcome in patients with non-metastatic osteosarcoma.(c) 2008 Wiley-Liss, Inc.