Introduction: Breast cancer diagnosed within 10 years of parturition is named postpartum breast cancer which is a highly metastatic tumor with poor prognosis. Case Report: A 31-year-old female presented with fever and painful mass in the left breast. She had undergone C-section 6 months ago of her second child. A left breast biopsy was performed and showed estrogen receptor-negative, progesterone receptor-negative, and human epidermal growth factor receptor 2 (HER2) negative invasive highly differentiated carcinoma. A radical mastectomy and left axillary lymphadenectomy were then performed and the anatomopathological report showed a 16cm metaplastic breast carcinoma. Eight months after the start of the chemotherapy treatment, the patient was diagnosed with brain metastases. Discussion: Postpartum breast cancer is associated with worse survival rates presenting increased risk of death. Metaplastic breast carcinoma is a subtype of triple-negative breast cancer also associated with poor prognosis and chemotherapy treatment resistant, being surgery the standard treatment.