First of all your question and purpose is not clear. You mean you want to inject tumor cells in to spleen and then sacrifice the mice after 12 hour and check the liver to see how many cells have reached the liver. That is not metastasis experiment. If you inject some tumor cells into spleen no cells will reach in liver within 12 hours. If you inject highly metastatic hepatocellular carcinoma cell line (HCC) along with high concentrated Matrigel,  it may develop into tumor and may metastasize to liver within 3 months. But chances of happening such things are rare and it depends on so many factors. Regarding labeling you can stably transfect the cells either with mCherry or tdTomato. Right now I am doing this experiment in our laboratory in Mayo Clinic. I am inducing intrahepatic tumors using HCC cells lines in nude mice.

As Joseph mentioned, the question you pose is not clear. When you talk about metastasis, it is a process that takes place gradually with time. For cancer cells to migrate from the spleen to the liver, a primary tumor will have to be induced in the spleen only then you can be certain that your cells are migrating to the liver. So certainly, you won't get anything out of your 12 hour time point. The time point will have to be at least a few weeks (3-4) long.

As far as labelling is concerned, do you have an in vivo small animal imaging system? If yes, that would solve your entire purpose of monitoring metastasis. You could stably transfect your cells with single (luciferase preferred over fluorescence) or dual reporters (luciferase and fluorescence) to monitor tumor growth and metastasis in vivo.

Also, after metastasis has occurred, you could also perform just the H&E staining to identify cancer cells in the liver.

Oh I am sorry if I confused you, and thank you for your answers!

However, there is an established method for liver metastasis through splenic injection of cancer cells,

By this method, cancer cell will reach the liver in several hours, (of course it takes about 3 weeks to develop cancer in the liver)

The purpose of the experiment is to check the quantity of cancer cells which "reached "the liver  instead of evaluating liver metastasis, 

Unfortunately I don't have any animal imaging system, thus I am considering this kind of methods,

Please let me know if you have better idea!

Thank you again!

Dear Hwijin i know this model of liver colonization by the spleen but as said Amirali and Joseph i dont' think that after 12 hours you can observe already the metastasis formation i use this model and after ten days i remove the spleen to observe metastasis in liver. For what concern the labeling of cancer cell i use cancer cells transfected with GFP or RFP that you can see with macroscope at fluorescence or with immunofluorescence.

Dear Antonio Barbieri

Thank you for your concern

I think that I have failed to convey my intention

Please check this article [Mol Cancer. 2015 Dec;14(1):282]

They have done what I am now trying to do with cell tracker

I will consider transfection as well thank you,