Coexistence of primary bone tumours: Report of 4 cases of collision tumours

Objective: To report, in 4 patients, the occurrence of 2 different primary tumours in proximity in the same bone. Three patients had osteosarcomas, and 1 had a giant cell tumour; all had coincident metaphyseal fibrous defect. Methods: Four patients (2 women, 1 man and 1 boy; 18, 25, 24 and 10 years of age, respectively) presented with progressive pain in the knee and distal thigh. All were studied by radiography, magnetic resonance imaging was done in 3 patients, and diagnostic open biopsy was performed for all. Results: Radiologic studies demonstrated tumours in the distal end of the femur in all 4 patients. Biopsy tissue showed a metaphyseal fibrous defect in all, with coexistence of an associated giant cell tumour in 1 patient and an osteosarcoma in each of the others. In all cases, the metaphyseal fibrous defect was penetrated by the adjacent tumour. Conclusions: Despite the relative prevalence of metaphyseal fibrous defect, giant cell tumour and osteosarcomas in the distal end of the femur and their occurrence in approximately the same age group, their association has rarely been reported. As both giant cell tumours and osteosarcomas are usually diagnosed late in their clinical course, they may outgrow and destroy any evidence of pre-existing metaphyseal fibrous defect. The rate of destruction is also influenced by the distance between the 2 lesions - the shorter the distance, the earlier the destruction.