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[[Tumor-to-tumor metastasis inside a meningioma]]
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Tumor-to-tumor metastasis (TTM) is defined as the hematogenous metastasis within a primary host tumor from a donor neoplasm. Although the precise mechanism of TTM is still unclear, it has been reported in the literature for over a century
((Moody P, Murtagh K, Piduru S, Brem S, Murtagh R, Rojiani AM. Tumor-to-tumor metastasis: pathology and neuroimaging considerations. Int J Clin Exp Pathol. 2012;5(4):367-73. Epub 2012 Apr 16. PMID: 22670183; PMCID: PMC3365818.))
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There is a difference between [[Tumor]]-to-tumor [[metastasis]] and [[collision tumor]]s. The former implies a recipient role of the host tumor, and the latter refers to a co-[[localization]] of two different tumors that grow into one another, both being in the same organ.
[[Tumor]]-to-tumor [[brain metastasis]] is a well-described [[phenomenon]] but with unclear [[pathophysiology]]. Deeper knowledge could be beneficial for its [[management]]
((Papadakis BK, Vorrias E, Bräutigam K, Chochlidakis N, Koutsopoulos A, Mavroudis D, Vakis A, Tsitsipanis C. Intrameningioma metastasis: A case-based literature review. J Clin Neurosci. 2021 Nov;93:168-173. doi: 10.1016/j.jocn.2021.08.028. Epub 2021 Sep 21. PMID: 34656242.)).
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lung cancer and breast cancer are the most common donor tumors in TTM 
((Lanotte M, Benech F, Panciani PP, Cassoni P, Ducati A. Systemic cancer metastasis in a meningioma: report of two cases and review of the literature. Clin Neurol Neurosurg. 2009;111:87–93.))
((Turner N, Kaye AH, Paldor I. Metastases to meningioma-review and meta-analysis. Acta Neurochir (Wien) 2021;163:699–709.))
((Papadakis BK, Vorrias E, Bräutigam K, Chochlidakis N, Koutsopoulos A, Mavroudis D, et al. Intrameningioma metastasis: a case-based literature review. J Clin Neurosci. 2021;93:168–173.)).