Nodular hidradenoma arising on the site of a BCG scar

Hidradenomas are tumours that arise from the adnexal structures, both eccrine and apocrine and are histologically benign. The tumours that arise from eccrine differentiation are known as poroid hidradenomas and when they arise from the apocrine glands they are called nodular hidradenomas. In our centre a 13-year-old boy presented with a slow-growing, painless erythematous fungating nodule on the left upper arm over a period of 18 months at the site of the BCG vaccination. The nodule was surgically excised and sent for histopathological examination, leading to a diagnosis of nodular hidradenoma. This case is presented to highlight its rarity, together with its clinical features that were suggestive of malignancy but proved ultimately to be benign.