Study of the Impact of DPD Activity on the Efficacy of Capecitabine

Inclusion Criteria: * Age over 18, * Performance status 0 to 2, * Patients with metastatic HER2 negative breast cancer, * Patients eligible for capecitabine monotherapy at a dose of 2000 mg / m² / day, 14 days every 21 days, * Determination of Uracil level performed according to national recommendations, * Patients with at least one lesion evaluable according to the RECIST criteria 1.1, or presenting at least 1 hypermetabolic lesion on PET-TDM according to PERCIST 1.0 criteria. In the case of single cutaneous metastasis (s), it is required to make photographs of lesions with a measure of the lesions using a ruler, * Patients receiving social coverage. Exclusion Criteria: * Performance status\> 2, * Contraindication to capecitabine monotherapy at a dose of 2000 mg / m² / day, 14 days every 21 days, * Presence of untreated or uncontrolled symptomatic cerebral or leptomeningeal metastases (unstable corticosteroid requirements) and / or non-clinically stable in the 3 months prior to inclusion, * History of cancer, with the exception of cancers in complete remission for more than 5 years, totally resected cutaneous basal cell carcinoma, in situ carcinoma or in situ cervical epithelioma treated, * Vulnerable people