Simultaneous metastasized primary unknown signet ring cell carcinoma of the cervical lymph node and mucoepidermoid carcinoma of the parotid gland as double cancers.

Lymph node metastasis from signet ring cellcarcinoma (SRCC) primary unknown is extremely rare. We here report a case of primary-unknown SRCC that metastasized to the cervical lymph nodes, co-existing with mucoepidermoid carcinoma (MEC) of the parotid gland as a simultaneous double cancer. A 68-year-old female patient with right swollen cervical lymph nodes consulted our medical center. A diagnosis of bilateral cervical lymph node metastasis and a right parotid tumor was made. After bilateral neck dissection and right parotidectomy, the pathological diagnosis was SRCC of primary unknown with metastasis to the cervical lymph node and MEC of the parotid gland. Examination of the CRTC1/3-MAML2 fusion gene showed no relation between SRCC of primary unknown with metastasis to the cervical lymph node and MEC of the parotid gland. Ten months after the first treatment, there was recurrence in the left neck lymph node, and left neck dissection was performed. Fourteen months after the first treatment, the patient is alive and cancer-free. This case is the fourth report of SRCC with lymph node metastasis, and highlights the value of fusion gene detection to determine relatedness between simultaneous cancers. Moreover, such cases should be closely monitored for the subsequent appearance of distant metastases.