Primary parotid adenocarcinoma metastasis to the spleen with PIK3CA mutation: cytological findings and review of the literature.

Background Primary solid tumor metastasis to the spleen is a rare event, and often presents as an incidental finding without clinical symptoms of the patient. The most common primary tumors that metastasize to the spleen are colorectal, ovarian, and lung carcinomas. Parotid tumor metastasis to the spleen is extremely rare. We report an unusual case of metastatic parotid adenocarcinoma NOS (not otherwise specified) to the spleen. Case report The patient presented with primary parotid carcinoma and underwent left parotidectomy. On pathological examination of the primary parotid tumor, no vascular or perineural invasion was found; all surgical resection margins and neck lymph nodes were also uninvolved by the tumor. No other therapy was given after the surgery. Four years later, the patient developed a solitary splenic lesion detected by a routine follow-up computed tomography (CT) scan. The subsequent fine needle aspiration (FNA) and splenectomy showed a metastatic adenocarcinoma consistent with the parotid primary. Immunohistochemical (IHC) staining of the metastatic tumor also showed a similar pattern as that of the primary tumor, including positivity for pancytokeratin, S-100 and SOX10, supporting the diagnosis. Furthermore, A PIK3CA (phosphatidylinositol 3-kinase catalytic subunit) mutation was also detected in the splenic metastasis. Conclusion Based on our review of the literature, we believe that this is the first report of such a case. Accurate diagnosis and molecular characterization of the splenic metastasis have a critical impact on the clinical management of the patient.