Intraductal carcinoma, apocrine type, of the parotid gland: A case report with pathological considerations

Intraductal carcinoma (IDC) of the salivary gland is a disease entity newly defined in the 4th edition of the WHO Classification of Head and Neck Tumors in 2017.Previously, it had been referred to as low-grade salivary duct carcinoma or low-grade cribriform cystadenocarcinoma.Here, we report a case of parotid gland carcinoma diagnosed as IDC.The patient was a 70-year-old man who presented to our department with a gradually enlarging mass in the right preauricular region for five months.Suspecting parotid carcinoma, we performed a superficial parotidectomy of the right parotid gland for both diagnostic and therapeutic purposes.The tumor was adherent to the communicating branches between the zygomatic and buccal branches of the facial nerve, necessitating partial resection of the nerve.Histopathologically, the tumor was composed of mainly intraductal cribriform or papillary proliferation of tumor cells with apocrine differentiation and low-to high-grade atypia, leading to a diagnosis of intraductal carcinoma, apocrine type.This subtype requires careful differentiation from salivary duct carcinoma (SDC) , given their overlapping immunohistochemical features.Moreover, the apocrine type of IDC may represent a precursor lesion to SDC, and thus close long-term follow-up is warranted.