['To evaluate the results of controlled ovarian stimulation before chemotherapy for oocyte vitrification to preserve fertility in women diagnosed with cancer and compare them with a historical control group.', 'A retrospective, multicenter, observational study performed between March 2007 and January 2011.', 'University-affiliated infertility clinics.', 'Of 272 patients affected by cancer in our Fertility Preservation Program, 223 women underwent a stimulated cycle for oocyte vitrification according to our protocols before cancer treatment. Their results were compared with a historical control group of 98 patients diagnosed with male factor infertility who were stimulated for a conventional IVF cycle.', 'Controlled ovarian stimulation and oocyte retrieval.', 'Days of stimulation, total dose of gonadotropins, estrogen levels, and number of oocytes retrieved and vitrified.', 'No differences were found in days of stimulation, but significant differences in E(2) levels and the number of retrieved oocytes were measured, especially in the hormone-dependent cancer group.'] Is ovarian response to controlled ovarian hyperstimulation in cancer patients diminished even before oncological treatment?