Gassy and mild mid left back pain. colon cancer likely? could be other problems?

Depends : unless high risk family history for cancer, colon CA is relatively low risk at your age. If pain with eating, then gallstones, peptic ulcer or irritable bowel syndrome are far more likely.

Mot colon Ca: The colon which is in the peritoneal cavity when developing a malignancy can induce pain when there is a partially obstructing lesion. The pain is intra abdominal. Back pain is usually related to a lesion in the retroperitoneum behing the peritoneal cavity or to pain arising in the lumbar muscles of the back. Duodenum which is retroperitoneal can occassional cause gassy and back pain complaints