Langerhans cell histiocytosis (LCH) encompasses a group of disorders characterized by the proliferation and infiltration of Langerhans cells within internal organs and/or skin. There is often multiorgan involvement; isolated cutaneous LCH is less common. The aetiology of cutaneous LCH remains uncertain, and debate remains as to whether LCH represents a neoplastic condition or is simply reactive. We report a 53-year-old woman who developed isolated cutaneous LCH 15 months after being diagnosed with infiltrating ductal carcinoma of the left breast. The LCH was treated with topical imiquimod, resulting in clinical and histological resolution. Our case highlights the rare association between cutaneous LCH and breast carcinoma, and the clinical and histological response that can be achieved with topical imiquimod. After a diagnosis of LCH, patients require long-term follow-up, due to the risk of recurrence and/or development of a subsequent malignancy.