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Programmed death ligand 1 (PD-L1) dysregulation has been implicated in chronic inflammatory diseases, but its role in regulating intestinal mucosa inflammation is still unclear. The aim of this study was to assess PD-L1 expression in the intestinal mucosa of patients with refractory inflammatory bowel disease (IBD) compared to controls. We evaluated PD-L1 expression by immunohistochemistry in colectomy specimens of patients with ulcerative colitis (UC) and Crohn disease (CD) compared to controls. PD-L1 expression was assessed in colonic epithelium and inflammatory cells, along with the location of the inflammatory cells expressing PD-L1. All cases were stained with CD3, CD4, CD8, FOXP3, CD20, CD68, and CD90 immunostains to determine the types of cells expressing PD-L1. The UC group showed significantly higher PD-L1 expression in the colonic epithelium than both CD and control groups (both P 0.001), and CD was also significantly higher than the control group (P = 0.004). Both UC and CD groups showed similar PD-L1 expression in the inflammatory infiltrate but significantly higher than the control group (both P 0.001). Among both IBD groups, higher IBD activity was associated with higher levels of PD-L1 expression in the colonic epithelium (P 0.05) and inflammatory infiltrate (P 0.001). When comparing PD-L1 expression to lineage-specific markers, CD3+, CD4+ T cells, CD68+ macrophages, and CD90+ colonic stromal cells appeared to be expressing PD-L1. These findings implicate a role for PD-L1 in the dysregulation of the immune response in refractory IBD. Further studies are warranted to better understand the role of the immune regulatory pathways in intestinal mucosa.

B3 thymoma is a rare malignant type of thymic epithelial neoplasm found in the anterior mediastinum. Diagnosis of thymoma from fine needle aspiration (FNA) can be challenging due to the infrequency of sampling and its morphologic overlap with other entities such as squamous cell carcinoma, lymphoma or thyroid carcinoma. We report a case of B3 thymoma mimicking poorly differentiated thyroid carcinoma. We present its diagnostic pitfalls on cytology specimens, especially where it concerns identifying the correct location of the lesion, discuss the differential diagnosis, and correlation with the corresponding surgical resection specimen. A neck computed tomography angiogram (CTA) revealed a partially calcified 2.1 cm mass inferior to the left thyroid lobe in a 51 yr old woman being evaluated for stroke/TIA symptoms. She was referred for evaluation of the lesion. On the initial FNA and core needle biopsy, the lesion showed high-grade epithelioid cells with abundant lymphocytic infiltration and occasional necrosis, and was diagnosed as a high-grade carcinoma, favored to represent a poorly differentiated thyroid carcinoma considering the location on imaging. The patient subsequently underwent total thyroidectomy, central neck dissection, and thymectomy. Final surgical pathologic diagnosis indicated a type B3 thymoma. Due to the infrequency of sampling, thymoma poses a diagnostic challenge on preoperative FNA or core needle biopsy. Herein, we present a case of B3 thymoma with a preoperative cytologic specimen that consisted of hyperchromatic sheets of epithelioid tumor cells with a background of lymphocytes without definitive follicular cells or colloid. The core needle biopsy and cell block material showed abundant necrosis, intermixed lymphocytes and neoplastic epithelial cells with strong positive staining for pan-keratin and p40. The cytology and core needle biopsy material were interpreted as representing a probable thyroid neoplasm and raised a broad differential including anaplastic thyroid carcinoma, poorly differentiated thyroid carcinoma with squamous features, metastatic squamous carcinoma, and metastatic carcinoma to a lymph node. The final surgical resection specimen showed a B3 type-thymoma.