This study is a prospective, multicenter study in which a serum sample will be collected at the day of starting neo adjuvant treatment in breast cancer patients

Inclusion Criteria:

• Women with a new diagnosis of triple negative breast cancer who have not yet started systemic treatment.
• Patients with stage I-III disease, patient with locoregional recurrence who have not been treated with chemotherapy before. ,
• Aged < 60 years
• Women having a (regular) physiological menstrual cycle
• Patients who are assigned to receive neoadjuvant chemotherapy with or without immunotherapy, targeted therapy and endocrine therapy
• Patients must be systemic treatment naïve for current malignancy (e.g. no chemotherapy, hormonal therapy or targeted therapy)
• Signed written informed consent

Exclusion Criteria:

• current use of hormonal contraception or in the six weeks prior to start of neoadjuvant systemic treatment for breast cancer, such as:

• Oral contraception (OAC)

• Hormonal intra-uterine device (IUD, Mirena)

• No ovarian function suppression to preserve fertility

• Other forms of hormonal contraception, including but not limited to: nuva-ring, Implanon, prikpil

• Currently pregnant and / or breast feeding. In case of use of hormonal contraception or breast feeding in de last year: patients should have had at least 2 menstrual cycles since stopping hormonal contraception.

  - active other malignancy

• IVF-trajectory for egg cell preservation prior to start of neoadjuvant systemic treatment

will follow