From the American National Cancer Institute:
The National Cancer Institute, a component of the National Institutes of Health, estimates that, based on current rates, 12.7 percent of women born today will be diagnosed with breast cancer at some time in their lives.
In AIS women the risk of gonadal cancer is less than 9%… see Karkazis, Fixing Sex, p308, note 15.
Why are women not subjected to routine breast removal given the higher cancer risk? The obvious answer is that it is as socially unacceptable for a woman not to have breasts as it is for a woman to have testicles.
Breasts are retained or substituted with artificial prostheses if they are removed. Testicles are removed as soon as medicine becomes aware a woman has them. Cancer is the scare used to convince the woman she should agree to be castrated.
Update and more information
Data on rates of gonadal cancers associated with AIS are scarce. Over time, known rates have declined and, in June 2019, a management protocol for retention of gonads was published: Weidler, E. M., Linnaus, M. E., Baratz, A. B., Goncalves, L. F., Bailey, S., Hernandez, S. J., Gomez-Lobo, V., & van Leeuwen, K. (2019). A Management Protocol for Gonad Preservation in Patients with Androgen Insensitivity Syndrome. Journal of Pediatric and Adolescent Gynecology, 32(6), 605–611. https://doi.org/10.1016/j.jpag.2019.06.005