The PIG-A gene (in humans)/Pig-a (in rodents) may be a useful reporter of acquired gene mutation. A simple and reproductive test based on flow cytometry allows detection of Pig-a mutants in a few minutes with low blood volumes. Many studies in rodents showed that detecting Pig-a mutations is useful for identifying genotoxic exposure, but studies are needed in humans to validate this biological marker. The investigators propose to carry out a study to assess the prevalence of PIG-A mutated reticulocytes among 30 patients exposed to genotoxic chemotherapy for breast cancer treatment. The investigators will prospectively collect, for each patient, 4 blood samples of 10mL during chemotherapy: the first one (T0) before chemotherapy (before genotoxic exposure), T1 during treatment (after the third cure), T2 (just at the end of chemotherapy) and T3 (five weeks after the end of chemotherapy). PIG-A mutated cells frequency distributions will be compared between T0, T1, T2 and T3. At the same time, the investigators will document the impact of such a genotoxic exposure using the micronuclei test on in vitro binucleate lymphocytes. The micronuclei test reveals structural or numerical chromosome aberrations caused by aneugenic or clastogenic exposure. This test will be done on T0 and T3 blood samples of each patient.

Inclusion Criteria:

• Major patients
• Patients with breast cancer
• Who have benefited from breast surgical treatment and have a poly-chemotherapy adjuvanted by FEC100 and Docetaxel.
• Patients should be able to read and understand French.

Exclusion Criteria:

• Minor Patients
• Pregnant women
• Patients who do not speak French and/or are unable to read and understand French.
• Patients who have had a history of radiotherapy, including those who have received a per-operative radiation therapy as part of the initial management of breast cancer
• Patients who have had a history of chemotherapy outside of the chemotherapy possibly received in the treatment of current breast cancer.