Malignant Transformation of Retroauricular Hidradenoma in Hidradenocarcinoma in a Nine-Year-Old Patient: A Case Report.

Hidradenocarcinoma, a rare malignant entity that derives from sweat glands, is especially rare in the pediatric population. The treatment of choice is surgery. Radiation therapy is used only in selected patients. Chemotherapy is not used extensively because its effectiveness has not been demonstrated yet. This case report describes a nine-year-old female patient who presented in 2018 with a vegetative lesion in the right parietal region. After excisional surgery, pathology confirmed that the lesion was a benign hidradenoma. However, the lesion recurred six months later, and subsequent surgery revealed nodular hidradenoma with positive margins. In July 2019, a new heterogenous lesion appeared in the right retroauricular region, which was surgically removed. The pathology report found possible malignant characteristics, and the patient was referred to our hospital where she was diagnosed with poorly differentiated right retroauricular carcinoma with infiltrative and perineural permeation, along with homolateral lymph node metastasis. It was histologically compatible with a hidradenocarcinoma. The patient underwent a wide-margin excision and homolateral total cervical lymphadenectomy, followed by adjuvant radiotherapy. The last follow-up MRI was negative for disease recurrence or metastasis; however, a slow-growing node on the left jugular chain (level II) was noted. The patient is on regular follow-ups to monitor disease status and treatment-related adverse events. This case highlights the challenges of diagnosing and treating hidradenocarcinoma, a rare malignancy that requires aggressive management with a multidisciplinary approach. More robust clinical evidence is needed to define the best treatment approach for these aggressive tumors.