Is air bubbles in urine a sign of colon cancer?

Not necessarily: Air bubbles when urinating implies a connection between the bladder and the colon (colovesical fistula), often seen with diverticular disease, and with advanced colon cancer. If there is a lot of bubbles in the bowl following urination, it may be normal, or may suggest increased amount of protein being voided.

Not necessarily: It is an abnormal sign that suggests a connection from the rectum into the bladder. Diverticulitis may have caused this, not a cancer. Best to seek workup and surgical correction soon to avoid chronic bladder infection that will result if not treated.