Visceral Metastases of Osteosarcoma in the Hepatopancreatobiliary System

<b>Background:</b> Osteosarcoma (OS) is the most common primary malignant bone tumor, mainly affecting adolescents and young adults. While lung metastases are common, visceral metastases in the hepatopancreatobiliary system are extremely rare and usually associated with a poor prognosis. The limited diagnostic and therapeutic options for such metastases make the treatment of affected patients difficult. The possibility of very late metastatic onset in high-grade OS highlights the potential need for extended follow-up (FU) beyond established intervals. <b>Methods:</b> This study combines a retrospective analysis of prospectively collected data from the Vienna Bone and Soft Tissue Tumor Registry with a review of the literature of patients with OS and metastases to the hepatopancreatobiliary system. A descriptive statistical analysis is presented for the entire cohort. In addition, publications from scientific databases (PubMed, Embase) were analyzed to evaluate the frequency, diagnosis, therapy, and prognosis of visceral metastasis from both conventional OS and primary extraskeletal osteosarcoma (ESOS). <b>Results:</b> A total of six male patients with conventional OS and metastases in the liver (5) and pancreas (1), with a mean lesion size of 38 mm (range, 10-120), were included. The median age at the time of visceral metastasis was 29 years (mean, 32 years; range, 20-62 years), and the mean interval since initial diagnosis was five years and ten months (range, 9 months-10 years and 9 months). Visceral metastases are very rare in general and usually occur in advanced stages of disease. We identified 51 cases of visceral metastases from conventional OS and 34 cases of ESOS in the hepatopancreatobiliary system in the literature. The metastasis interval was three years (range, 15 months before diagnosis-17 years) at a median age of 27 years (mean, 32 years; range, 10-69 years). <b>Conclusions:</b> Visceral metastases from OS are rare but represent a significant therapeutic challenge. Early, targeted imaging in combination with improved methods for diagnosis confirmation and interdisciplinary treatment strategies may potentially improve the results. This study underlines the importance of early diagnosis and highlights the need for individualized long-term surveillance strategies exceeding ten years, especially in high-grade OS, aiming at early detection of late-onset metastasis.