Your doctor may be trying to ease your mind, but if he or she is telling you that the side effects are hypothetical, that doctor is misinformed or lying. The FDA is clear that they are not hypothetical, and duration is considered a factor in carcinogenesis.
Your concerns are well founded, and I understand the many reasons doctors brush off patient concerns, but I'd be looking for another doctor if I were that uncomfortable with mine. They are practitioners of a skill set, nothing more.