Aims. The aim of this study was to assess the clinical and radiological outcomes of an antiprotrusio acetabular cage (APC) when used in the surgical treatment of periacetabular bone metastases. Methods. This retrospective cohort study using a prospectively collected database involved 56 patients who underwent acetabular reconstruction for periacetabular bone metastases or haematological malignancy using a single APC between January 2009 and 2020. The mean follow-up was 20 months (1 to 143). The primary outcome measure was implant survival. Postoperative radiographs were analyzed for loosening and failure. Patient and implant survival were assessed using a competing risk analysis. Secondary parameters included primary malignancy, oncological treatment, surgical factors, length of stay in hospital, and postoperative complications. Results. A total of 33 patients (59%) died during the study period at a mean of 15 months postoperatively (1 to 63). No patient had radiological evidence of loosening or failure. Acetabular component survival was 100%. Three patients (5.4%) had further surgery; one (1.8%) underwent revision of the femoral component for dislocation, one required debridement with implant retention for periprosthetic joint infection, and one required closed reduction for dislocation. Using death as a competing risk, at 100 months, the probability of revision was 0.036 and the risk of death was 0.84. Conclusion. With appropriate patient selection, the antiprotrusio cage offers good implant survival, with a reasonable perioperative complication rate in this high-risk group of patients when managing metastatic disease or haematological malignancy around the acetabulum. Cite this article: Bone Joint J 2022;104-B(4):504–509