Immunohistochemical analyses have shown that SDC typically demonstrates and usually expresses AR, CK7, CK AE1/3, GCDFP-15, 34bE12, EMA, and CEA. Occasionally, it can be positive for S100, ER and PR. AThe androgen receptor is expressed significantly more often in salivary duct carcinomas of men than in salivary duct carcinomas of women. Expression of CK7 and HMWKs support the diagnosis of salivary duct carcinoma. In the present case, we found that tumor cells were positive for cytokeratin (Ck 7, Ck HM), S-100 protein, and Vimentin.
The differential diagnosis of salivary duct carcinoma includes metastatic breast and squamous carcinomas, adenocarcinoma, adenoid cystic carcinoma, mucoepidermoid carcinoma, basal cell carcinoma, small cell carcinoma (neuroendocrine carcinoma), and sinonasal undifferentiated carcinoma.
Despite a superficial resemblance to squamous carcinoma, this diagnosis can be discarded as soon as the infiltrating cribriform pattern is recognized. Goblet cells are not seen with SDC, thus ruling out mucoepidermoid carcinoma. Pleomorphism, mitotic activity, and comedonecrosis are characteristics of SDC that distinguishes it from adenocarcinoma of the salivary gland. In addition, besides tumor cell morphology, lack of p63 and CD-117 expression also rules out of adenoid cystic carcinoma. Small cell carcinoma is composed of sheets of hyperchromatic round to oval to spindle cells with minimal cytoplasm, inconspicuous nucleoli, and focal necrosis. They are immunoreactive to CK 20 and EMA, thus differing from SDC. Basal cell carcinoma produces basement membranelike material and has cribriform and solid areas. It reveals greater nuclear pleomorphism, squamous differentiation, prominent necrosis, and frequent mitoses and also shows focal keratinisation the presence of surface squamous dysplasia, in Ssitu, or invasive carcinoma.
Imaging findings, especially CT scan and MRI are non-specific, although they can indicate the malignant nature of the tumor by showing ill -defined borders, or an infiltration of the adjacent tissue. Positive diagnosis is based on histologic examination.
The prognosis for salivary duct carcinoma is poor. Most of the cases reported in the literature have an aggressive nature with an average survival period of about the first 5 years after diagnosis, and the death rate has been reported to be 60-80% of the patients. Local invasion, frequent lymphatic and hematogenous metastasis characterize the biologic behavior of salivary duct carcinoma. Some studies described some correlation of prognosis to tumor size (less than 3 cm indicated a better prognosis).
In summary, SDC is an uncommon tumor in minor salivary glands. Although, iIt is aggressive and has a high possibility of developing local and distant metastasis, besides several factors, anatomical location, and clinical stage of the tumor are relevant and may interfere with the clinical course of the tumor.