What is the dependence and correlations between cancer and radiation?
Usually cancer is coming due to accumulation of mutation in certain genes and you need at least 5-7 different mutations that are really necessary to trigger cancer development. And any factor that is triggering mutation can of course increase a probability of cancer development. So of course in case of such high radioactive dose and exposure it obviously can increase a probability of cancer development especially thyroid cancer and leukemia.
Is it possible to develop mass cases of cancer due to the radiation exposure?
Yes, obviously yes.