Non-Hematological Primary Source of Bone Marrow Metastasis in Adults: A Systematic Review

Introduction: In recent years, scientific interest in bone marrow invasion or infiltration by non-hematological malignant cells has increased due to growing evidence suggesting a prognostic impact in certain specific types of solid tumors. However, the available data on the primary source of metastasis are scarce. Objective: synthesize the reported data on non-hematological tumors infiltrating the bone marrow in studies based on histopathological confirmation of metastases. Methodology: PubMed/Medline and Google Scholar were used for the systematic review; the filters used were human studies, adult age (>14 years old), and the period between 1990-2021. The main inclusion criteria was the histopathological confirmation of bone marrow invasion. The exclusion criteria were small case reports, specific neoplasm criteria, and grou-ped case series in secondary literature to minimize bias. Three different researchers evaluated all the titles and abstracts available. Two researchers independently extracted and recorded data; this process was cross-checked again. Finally, data were summarized and presented in tables using descriptive statistics. Results: 31 articles from 12 countries were included; four were multicenter, and all but 2 were retrospective. One thousand four hundred fifty-one adult patients with Bone Marrow Metastasis due to solid tumors were found. All included studies presented the distribution of the primary source of metastases: 82 % were epithelial neoplasms, 14 % were tumors of unknown primary origin, and 10 % were low-frequency specific neoplasms grouped as ‘others’. Conclusion: The results can be considered with caution due to the methodological heterogeneity of the studies and the risk of bias.