Objective: to assess the preliminary surgical and functional results of using modular acetabular endoprostheses in cancer patients. Subjects and methods. In the period of 2011 to 2017, surgical treatment as periacetabular resection with reconstruction of the acetabulum and hip joint, by applying a modular endoprosthesis, was performed in 20 patients with locally advanced pelvic bone tumor. There were 12 (60%) women and 8 (40%) men. Primary bone tumors were present in 18 (90%) patients. Stages IB and IIB were detected in 2 (10%) and 11 (55%) patients, respectively. Stage III was identified in a female patient with synovial sarcoma of the soft tissues in the periacetabular region. Results. The mean duration of surgery was 310 min; the mean intraoperative blood loss was 3000 ml. The scheduled postoperative morphological examination revealed negative resection margins (R0) in 17 (85%) patients. A positive resection margin was seen in 3 (15%) patients. The mean follow-up period was 36 months. The progression of the disease was diagnosed in 8 (40%) patients within 6 to 25 months. All these patients had primary malignant tumors of the bones (n=7) and soft tissues (n=1). Four patients were diagnosed with distant metastases: 2 patients had the latter with a tumor recurrence and 2 had that with a localized recurrence. After surgery, the mean Musculoskeletal Tumor Society Rating Scale (MSTS) score was 59%. Postoperative complications were diagnosed in 9 (45%) patients. Revision surgery due to complications was performed in 5 (25%) patients; 3 (15%) of them required removal of a prosthesis. Conclusion. Modular prosthetic replacement of the periacetabular region is the newest technique that has been widely used in specialized clinics in the past 10-15 years. Its chief difference from other previously used repairs is the ability to intraoperatively collect an individual endoprosthesis that maximizes all the peculiarities of the operation and allows the planning of pelvic bone resection margins depending on the specific clinical situation.