What does it mean for bladder cancer to be anaplastic?

See explanation. Anaplastic is a descriptive term for the microscopic appearance of the tumor which may also be labelled "poorly differentiated". This typically translates to more aggressive behavior in the general sense. It means that the tumor cells look very unlike normal bladder cells and the more that is true, the more aggressive the tumor may behave. This holds true for most types of cancer.
Anaplastic meaning. When a tumor is anaplastic, it means that it no longer looks like normal tissue. Tumors that are anaplastic are more aggressive and tend to have poorer outcomes.