The Female Man by Joanna Russ asks just that question. I picked up the book after seeing an article following her death in April this year. I feel ashamed to admit I’d never heard of Ms Russ prior to that, especially given that she is hailed as the forerunner of feminist science fiction writing and cited as a significant influence on modern authors such as William Gibson. The Female Man was written in 1969/70 and published five years later in a literary genre dominated by men. It received a mixed response, but has since become an extremely well respected novel, nominated for the 1975 Nebula Award for Best Novel and then winning one of the three Retrospective Tiptree Awards in 1996.
I understand why it elicited strong responses, released as it was at the height of the second-wave feminist movement. In many ways it is more a study in feminism than a science fiction story, yet I’m not sure where else it might be fit if not as Sci-Fi.