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Triple-negative breast cancer (TNBC) is an aggressive subtype with high recurrence risk. The KEYNOTE-522 trial demonstrated improved pathological complete response (pCR) rates and survival outcomes with the addition of pembrolizumab to neoadjuvant chemotherapy. However, long-term immune-related adverse events (irAEs) remain a concern, particularly in curative settings. We report a case of a woman in her early 40s with node-positive TNBC who achieved a pCR following neoadjuvant chemoimmunotherapy. After completing adjuvant pembrolizumab, she developed acquired lipodystrophy, an under-recognised irAE, manifesting as progressive subcutaneous fat loss, dyslipidaemia, and hepatic steatosis. Histology demonstrated adipocyte necrosis with lymphohistiocytic infiltration. Corticosteroids stabilised progression but did not reverse changes. This case highlights the need for long-term surveillance of irAEs and raises important questions about immunotherapy de-escalation in patients achieving pCR, against a rapidly evolving systemic treatment landscape for TNBC.