A tumour-to-tumour metastasis, also known as a collision tumour, is a rare metastatic process in which a primary malignant tumour ('donor') metastasises to another tumour ('recipient'), most commonly a benign tumour such as a meningioma.
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Epidemiology
Tumour-to-tumour metastasis is considered very rare, with one review in 2012 uncovering only 84 cases in a literature search 1.
Clinical presentation
Clinical presentation is highly variable depending on the primary donor tumour and the tumour to which it is metastasising to 1-3.
Pathology
The most common recipient of these metastases are meningiomas with the most common donor tumours being breast and lung cancers, however many different donor (e.g. renal cell carcinoma, prostate cancer) and recipient tumours (e.g. renal cell carcinoma, thymoma, uterine leiomyoma) have been reported 1-4.
Meningiomas are the most common recipient tumour and although the reasons for why this is so remain unclear, it has been postulated that they have many characteristics that promote tumour growth, such as slow growth rate, hypervascularity, high collagen, and high lipid content 1.
Radiographic features
Similar to clinical presentation, radiographic features are highly variable and often CT and MRI alone are not sufficient to confidently make the diagnosis of tumour-to-tumour metastasis 1.
As meningiomas are the most common recipient tumour, they are most commonly described radiographically in the literature 1. In general, unusual radiographic characteristics and unexpectedly rapid growth in a meningioma may be prompts to consider this rare diagnosis 5.
CT
Appearance is variable, with the metastasis within a meningioma appearing as either hyperdense over the meningioma, or hypodense if it has a necrotic component 1.
MRI
Again highly variable, MRI reveals signal characteristics that are unusual for a meningioma 1. MR spectroscopy and MR perfusion may be additionally utilised to detect further characteristics atypical for meningioma 1.
Treatment and prognosis
Treatment involves resection, which is often necessary for diagnosis anyway, and management of the primary tumour 1. Prognosis is that of the metastasised primary malignancy.
History and etymology
Tumour-to-tumour metastasis was first described by Berent in 1902 4,6.
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