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

Abstract

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.

Keywords: Parotid adenocarcinoma; metastatic carcinoma; splenic metastasis.

Figure 1

The FNA smears of the splenic mass. A: The tumor cells are arranged in tubulopapillary and/or two-dimensional fragments. B: The tumor cells have enlarged round-to-oval nuclei, coarse chromatin, irregular nuclear membranes, prominent nucleoli, and occasional small cytoplasmic vacuoles.

Figure 2

Histomorphology of the surgical resected splenic metastasis. A: The tumor infiltrates into the splenic parenchyma without capsular formation. Tumor cells are arranged in sheets and clusters. B: Tumor cells have large hyperchromatic nuclei, coarse chromatin, irregular nuclear membranes and prominent nucleoli. Numerous mitotic figures are identified.

Figure 3

Histomorphology of the parotid adenocarcinoma. A: The parotid parenchyma is replaced by infiltrating clusters of malignant epithelioid cells. Most of the tumor demonstrates small glandular architecture separated by fibrous bands. B: The tumor cells are intermediate in size, with high nuclear/cytoplasmic (N/C) ratio and marked nuclear atypia.

Figure 4

IHC study of the splenic metastasis. A and B: The tumor is diffusely positive for pancytokeratin AE1/AE3 and SOX10. C: The tumor is focally positive for S100. D: GCDFP is predominantly negative.