A case of pulmonary metastasis with interstitial spread of sinonasal adenoid cystic carcinoma
A 64-year-old woman was diagnosed with sinonasal adenoid cystic carcinoma (cT4N0M0, cStage IVB) and received induction chemotherapy and proton beam therapy. Four years later, the first local recurrence was identified. At the same time, computed tomography (CT) showed a partial solid ground glass nodule (24 mm in size) in the right upper lobe; this lesion was suspected to be a primary lung adenocarcinoma, so a wedge resection of the right upper lobe was carried out. Grossly, the surgical specimen revealed a gray-white solid mass. Histologically, the mass was made up of atypical cells that proliferated in tubular, cribriform, and solid structures. At the lesion’s margins, tumor cells infiltrated the alveolar septa (known as interstitial spread), and the overlying pneumocytes showed hyperplastic changes and nuclear atypia. Two cell types were identified using immunohistochemistry. One was a distribution of epithelial cells with cytokeratin (CK) 5/6, CK AE1/AE3 positivity. The other was the proliferation of cells with positive myoepithelial markers, such as p40, p63, and αSMA. The lesion’s myoepithelial cells also tested partially positive for C-Myb. TTF-1 and Napsin A were positive for overlying pneumocytes but negative for tumor cells. Based on the above findings, we diagnosed pulmonary metastasis of sinonasal adenoid cystic carcinoma. Metastatic tumors with interstitial spread and pneumocyte hyperplasia appear to be rare. The disparity between the chest CT image and the pathology findings could be attributed to this distinct growth pattern; however, more data to confirm this relationship needs to be collected.
