Mammary Analogue Secretory Carcinoma Presenting as a Cervical Lymph Node Metastasis of Unknown Primary Site: A Case Report

BACKGROUND: Mammary analogue secretory carcinoma (MASC) is a pathological entity arising in the salivary glands first described by Skalova et al. [Am J Surg Pathol 2010;34: 599–608]. Here, we report the first case of MASC presenting as a cervical lymph node metastasis of unknown primary site together with a brief review of the literature. CASE REPORT: We present a 74-year-old male with a painless lump in his left neck. Based on the fine-needle aspiration cytological findings, a possible malignant tumor was suspected. No evidence of a primary lesion was observed using imaging modalities including positron emission tomography/computed tomography. The patient underwent an ipsilateral modified radical neck dissection. Immunohistochemical staining showed that the neoplastic cells were positive for S100 protein and GATA3. A rearrangement of the ETV6 gene was noted during fluorescence in situ hybridization, and the final histopathological diagnosis was MASC. CONCLUSION: We encountered a MASC presenting as a cervical lymph node metastasis of unknown primary site. No adjuvant therapy was administered, and no local recurrence or metastatic disease has been detected during a follow-up period of 9 months. This is the first case report of MASC presenting as a cervical lymph node metastasis of unknown primary site and suggests the new properties of MASC.