When cancer has not spread beyond its site of origin a complete cure is often possible. When a cervix cancer is localised, almost 100% cure is possible but when it has spread to nearby bladder or rectum, not even 20% will live upto 5 years. Similarly, an early breast cancer when treated adequately, would have a more than 85% chance of surviving more than 5 years whereas when it is spread to lungs less than 10% would survive 5 years. Thus early diagnosis ensure a better cure rate.
No pain is not a symptom of early cancer, it is a symptom of advanced cancer.