A 76-year-old man comes to see you. He has not been sexually active for some years and he is obviously embarrassed to tell you that he thinks he has developed some form of sexually transmitted disease. He assumes this because he has found an ulcer on his penis. Indeed there is an irregular 1-2cm ulcerated area on his penis and you think he has inguinal lymphadenopathy as well. You are concerned that this could be penile cancer. Which of the following assertions is incorrect ?