The main objective of the study is to evaluate the overall survival and disease-free survival in breast cancer patients under 40 years old. They underwent controlled ovarian stimulation (COS) for fertility preservation versus women of the same age, type and stage of breast cancer, who have not been subjected to COS.

Breast cancer is a disease where the tumor size, lymph node involvement and histological grade provide rich information about prognosis and enable to stage the disease. As in any other oncological pathology, stage of disease at diagnosis is the major determining factor for estimating survival. Ovarian stimulation for fertility preservation is performed in this study, in patients with stage I-II (TNM) after the neoplasia is treated (surgical removal of the tumor) prior to systemic therapy, when indicated.

Among young women there is a greater incidence of basal type tumors and HER2 (human epidermal growth factor receptor 2), which do not always express hormone receptors. In early stages of the disease, the controlled ovarian stimulation procedure, after removal of the tumor, has not revealed any worsening in the prognosis of the disease, in terms of overall survival and disease-free survival (absence of local or distant recurrence).

It is a study that aims to collect data retrospectively from 2008 to 31 December 2015. To this end, we will collect the follow-up data, up to 5 years for patients from 2008, 2009 and 2010. Four years for patients in 2011, 3 years for 2012, 2 years for 2013, one year for those included until 31 December 2014 and patients followed until 31 December 2015. Each patient is called in order to request data authorization, to complete and track information.

Inclusion Criteria:

• Age under 40 years ( at the time of diagnosis)
• TNM stage I- II
• Authorization of the fertility preservation multidisciplinary committee

Exclusion Criteria:

• Contraindications for pregnancy
• previous history of infertility
• Previous history of ovarian surgery
• Prior chemotherapy
• History of pelvic radiation
• Diabetes Mellitus
• Hypertension
• renal failure
• liver failure
• autoimmune disease.

Age under 40 years ( at the time of diagnosis) TNM stage I- II Authorization of the fertility preservation multidisciplinary committee