Unicystic high-grade intraductal carcinoma of the parotid gland: cytological and histological description with clinic–pathologic review of the literature

Intraductal carcinoma of the salivary glands is a rare, not well-characterized tumor. We reviewed the literature and report the first case of a high-grade unicystic intraductal carcinoma of the parotid. Formalin-fixed/paraffin-embedded blocks were sectioned and stained for hematoxylin and eosin and immunostains (CAM5.2, EMA, CK5, p53, p63, SMA, S100 protein, DOG1, mammaglobin, AR, ER, PR, Her-2, and Ki67). A 72-year-old man showed a painless nodule (2 cm) in the right parotid region. A ‘tumor of uncertain malignant potential’ (low grade) was diagnosed by fine-needle aspiration cytology (FNAC). Preoperative magnetic resonance imaging revealed a well-delimited, oval cyst without evidence of parenchymal invasion (T1-scans: homogeneously isointense with hypointense thin peripheral ring; T2-scans: strongly hyperintense). Histological examination confirmed a unilocular cyst lined by a multistratified epithelium arranged in solid, pseudopapillary, cribriform, and ‘incomplete cribriform/microcystic’ patterns. Tumor cells were CAM5.2+, EMA+, mammaglobin+, AR+, p63+ (focal), CK5+ (focal), p53 (+, 20%), ER-, PR-, S100 protein-, DOG1-, and Her-2-. A continuous peripheral layer of p63+/CK5+/SMA+ myoepithelial cells proved the ‘in situ’ nature of the tumor. The evidence of focal severe nuclear atypia, high mitotic index (12 mitoses/10HPFs), and high proliferation index (40%) favored a high-grade intraductal carcinoma. Preoperative FNAC and clinic–pathologic correlation are very helpful. Discrepancy in dysplasia grade between FNAC and resected specimen can occasionally occur (especially in case of focal high-grade features). Total sampling should exclude invasive areas or other cystic malignancies.