Dictionary<> fun

Here is a brief trivia. Take a look at this piece of code:

Dictionary<Tubo, object> dictionary = new Dictionary<Tubo, object>();
Tubo tubo = new Tubo();
dictionary.Add(tubo, new object());
// some code here and there
bool keyExists = dictionary.ContainsKey(tubo);

Basically I create a Dictonary instance and I use a class Tubo as a key type. I create an instance of Tubo (which is used as a key), add it to dictionary, run some code and then check whether key (same instance as above) is still there.

Is it possible that I get keyExists == false (note that Tubo instance is the same)?