Pruritus is a debilitating symptom that can be associated with cutaneous involvement by an underlying malignancy. We report the case of a 68-year-old woman with a history of triple-negative breast cancer who presented with extensive, localised cutaneous metastasis complicated by incapacitating, treatment-refractory pruritus localised to the anatomic regions involved by her metastatic disease. Physical examination revealed an indurated, ecchymotic, ulcerated plaque circumferentially encasing her thorax. Histopathological examination revealed substantial dermal lymphatic involvement and dilation as well as dermal collagen infiltration by tumour cells and nodules. The clinical and pathological findings were consistent with a diagnosis of carcinoma en cuirasse. Mirtazapine, a noradrenergic antidepressant with antiserotonin and antihistamine activity, was started and led to rapid, sustained relief of the patient's pruritus. Mirtazapine may be a useful systemic agent for the palliative relief of pruritus associated with cutaneous infiltration by an underlying malignancy.