Gallbladder cancer is a common hepato-biliary disease associated with some other risk factors like chronic infections of the gallbladder. Studies have shown a relationship between mixed bacterial and Salmonella infections in the evolution of cancer gallbladder. So this bacterial degradation of bile along with chronic inflammation have, as a consequence, the appearance of fever as a typical symptom.
As mentioned before, this disease does not usually cause any symptoms in the early stages. It is often diagnosed at a more advanced stage. But, due to the risk factor associated with infections, fever is a symptom that might alert of possible danger if it noticed with some other early signs.