Hidradenocarcinoma over a Surgically Excised Hidradenoma of the Foot. A Case Report of a Very Rare Presentation of a Rare Tumor.

Introduction: Hidradenocarcinomas are very rare and aggressive soft-tissue tumors, originated from sweat gland cells, which are located most frequently in head and neck, being their appearance at the extremities rare. This kind of tumor usually appears de novo and very few cases have been reported until now of appearance over benign lesions such as hidradenomas. Malignancy progression rate of hidradenomas is unknown, and this benign lesion has clinical and histopathological characteristics in common with hidradenocarcinomas that could lead to misdiagnosis. Hidradenocarcinomas have a very poor survival rate; therefore, an early diagnosis is essential for a better prognosis, and that is the reason why hidradenomas should be widely excised from the beginning, instead of performing marginal resections of this lesions that could lead to an aggressive recurrence. Case Presentation: Here is a case report of a 27-year-old woman diagnosed with a hidradenocarcinoma over a previously excised hidradenoma in the right foot. The diagnosis was made after right pelvic and inguinal lymphadenopathies appeared few months after a new small asymptomatic lump appeared at the same place in the sole of the right foot were the excised hidradenoma five years before was located. Lymph node biopsy was performed, with histopathological diagnosis of hidradenocarcinoma metastasis. Surgical local wide excision of the lump at the foot and lymphadenectomies was performed. Histopathological analysis of the samples confirmed the diagnosis of hidradenocarcinoma. The patient later received adjuvant radiotherapy and after one year there are no signs of disease recurrence. Conclusion: Many questions remain uncertain about the management and treatment of hidradenocarcinomas due to the rarity of this type of tumor. Although targeted molecular therapies have shown promising results, more studies in this field are necessary. An early diagnosis and differentiation from its benign counterparts that allow local control of the disease before spreading is essential to improve survival rates.