There is a hadeeth where the Prophet salla Allahu alaihi wa sallam has told us that the martyrs except those who die defending Islam are many such as those who die with an illness that comes in the stomach, those who die in a fire or drowned.
Some scholars said that if the cancer is in the abdominal area, it falls under this hadeeth. Others said that this illness wan known to the Arabs and it is not cancer.
I believe that Allah’s mercy and generosity is endless.