Osteosarcoma in One of Identical Twins: Three Cases Report and a Literature Review.

Background: Osteosarcoma (OS) is the most common primary malignant bone tumor occurring mainly in children and young adults. OS is usually seen in sporadic cases, and it is an extremely rare phenomenon in blood relatives, particularly among identical twins.

Case Presentation: The present study reports three cases of OS occurring in only one of identical twins. The first case is a high-grade OS in the left proximal tibia of a 16-year-old girl, treated with neo-adjuvant chemotherapy, en bloc resection, and reconstruction with a modular knee tumor prosthesis. The second one is a high-grade OS of the left proximal tibia of a 6-year-old girl. The patient was treated with neo-adjuvant chemotherapy, en bloc resection, and reconstruction with inactived autograft. The third one is a conventional OS of the right proximal tibia of a 20-year-old woman. She was treated with neo-adjuvant chemotherapy, en bloc resection, and reconstruction with a custom-made prosthesis.

Conclusions: The occurrence of OS in one of identical twins is a relatively rare event but may present the best opportunity to understand the genetic mechanisms underlying the tumorigenesis and progression of this disease in humans. A longer follow-up period and regular imaging evaluation are needed to confirm whether the identical twin of these patients will suffer OS in the future.