EpCAM (MOC-31) - immunohistochemical expression in papillary thyroid carcinoma and non invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP).

Introduction: Ep-CAM, is a cell adhesion glycoprotein located on the basolateral cell membrane surface and in the cytoplasm of most normal epithelial cells. It has also been described to be expressed in several malignancies such as lung, digestive, prostate and renal carcinomas suggesting it has a potential role in carcinogenesis.  In thyroid carcinoma, Ep-CAM expression has rarely been studied especially in papillary thyroid carcinoma.

Objective: We sought to describe and compare the immunohistochemical expression of MOC31 in papillary thyroid carcinoma and in non invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP).

Methods: We have retrospectively collected 33 cases of PTC diagnosed in the pathology department of the Security forces hospital during a period of 13 years (2008-2021). We have microscopically reviewed all cases and reclassified 9 of 33 cases as NIFTP.  An immunohistochemical  automated study have been performed with MOC-31 antibody.  The immunostaining was considered positive when it was membranous and/or cytoplasmic. The intensity of staining was scored as weak (score 1), moderate (score 2), and strong (score 3). We have used an immunoscore for assessing level of expression of MOC31 as follows: 0 for <5% of positive cells, 1 for 5-30%, 2 for 31-50%, 3 for 51-70%.The total score resulted by summing the percentage score with the intensity score; the final score was varying from 0 to 7, considered low between 1-4 and high 5-7.

Results: The mean age of patients was 45,2 years-old for PTC cases and 48,1 years-old for NIFTP cases. A net female predominance was found in both groups (male to female ratio of respectively 0,4 and 0,3). MOC31 expression was found in 19 cases of PTC with a percentage of positive cells varying from 5 to 90%. Percentage of positive cells was variable from 5 to 90%. The immunoscore for positive cells was: 0 in 5/24cases, 1 in 4/24cases, 3 in 9/24cases and 4 in 6/24cases. The intensity of staining was assessed score2 (moderate) in 8 cases and score 3 (high) in 7cases (Figure1-2). Final MOC31 staining score was low in 37,5% (9/24) and high in 62.5% (15/24). Patients with advanced pt2-pt3 stages mostly showed high score of MOC31 staining (61,5%).One case was associated with lymph node involvement and was of a high score. 6 cases showed vascular invasion and was of high MOC31 score. MOC31 was expressed in all NIFTP cases with variable proportion of positive cells (5%-80%). The immunoscore for positive cells was: 0 in 1/9cases, 1 in 2/9cases, 2 in 3/9cases, 3 in 1/9cases and 4 in 2/9cases. The intensity of staining was assessed score 1 (weak) in one case, score 2 (moderate) in 6 cases and score 3 (high) in one case (Figure3-4). The final combined score was low in 66,7 (6/9) and high in 33,3% (3/9).

Conclusion: Our study revealed different immunohistochemical profile of MOC31 in benign and malignant tumors. It has somewhat a diffuse and marked staining in the first group.  The changes of MOC31 location as well as its score of staining in PTC and NIFTP could hence be helpful in the differential diagnosis. Our findings also support the potential prognostic value of this molecule that deserves further investigations.