Why is the choroid a common location for metastic cancers?

Choroid: Because there are a lot of blood vessels in the choroid. Cancer can spread through lymphatic organ or blood. Cancer can spread to the eye hematogenously/via blood and choroid would be the one that is affected the most.

Is it?: It may help if you could provide a source for the information. "choroid" is not a common site for mets.

Anatomy: While the choroid is not an extremely common site for metastasis, it is not rare. Why it happens is likely a combination of factors which include the specific nature of the particular cancer cells and the anatomy of the complex vessels of the choroid.

It isn't: The choroid is a rare site for metastatic cancers.

Blood supply: Metastatic tumors like to take up residence in richly vascularized tissue to give them a good blood supply. The choroid is a rich vascular network supplying the overlying retina and metastatic tumors gravitate towards this tissue.