Dr. Luce is the doctor in New York who is considered an "expert" in hermaphroditism. In the 70s, this medical concentration alone reveals Dr. Luce to be a "sympathetic" character. At that time, such sexual and genetic disorders were largely unexplored and unspoken of.
Dr. Luce originally misdiagnosis of the cause of Cal's mutation and incorrectly assumes he would rather be a woman than a man. He is not completely confident with his diagnosis, and even when publishing her case, he hopes Cal never shows up to refute the ideas presented. However, instead of presenting the doctor as judgemental, harsh, dismissive, or even fame-seeking, Eugenides shows him to come across as genuinely concerned for Cal's well-being. The audience believes Dr. Luce wants what is best for this patient who, through lying on many preliminary questions, suggests that her (his) natural sexual orientation tends to be that of a woman, not a man. In the end, the audience pities both Cal and the doctor with the understanding that neither can be fully open about the truth with one another because it seems socially inappropriate, awkward, and potentially destructive.