Although I've worked in radiology, I'm not a radiologist. I suggest you ask one to see if there are any visual clues that can distinguish a benign tumor from a malignant one. Or ask a pathologist if you're looking at biopsies instead of radiological images.
When I worked in radiology they didn't even like software to claim to make diagnoses (usurping their job). Software engineers were also reluctant to do so because of liability concerns. Would you want your software to claim it was benign, only to be sued when it turned out the patient died because it was actually malignant?