Unveiling molecular signatures in incidentally detected uterine adenomatoid tumors: An immunohistochemical analysis of L1CAM and BAP1

BACKGROUND: Uterine adenomatoid tumors (UAT) are rare, benign mesothelial tumors occurring in the vicinity of leiomyomas, adenomyosis, and endometriosis. Tumor biology of UAT remains poorly understood. Their diverse growth patterns may be mistaken for invasive malignancies on histology. The present study aimed to characterize the clinicopathological features of UATs, evaluate the expression of L1 cell adhesion molecule (L1CAM) and BRCA-1 associated protein 1 (BAP1), and assess the utility of conventional immunohistochemical markers in distinguishing UATs from their histological mimickers. MATERIALS AND METHODS: Histopathology archives of all hysterectomy and myomectomy specimens diagnosed as UAT from 2015 to 2022 were reviewed. Their clinical, radiological, and pathological features were analyzed along with the expression pattern of calretinin, D2-40, keratin 5/6, WT1, and BAP1. Prognostic and predictive markers, L1CAM and hormone receptor ER, were also assessed. RESULTS: Five cases were identified in patients aged between 29 and 55 years. Gross examination revealed ill-circumscribed gray-white masses, typically subserosal in location. Microscopically, they demonstrated cyst-like spaces within hyperplastic smooth muscle tissue. Calretinin and D2-40 showed diffuse, strong positivity, while WT1 and keratin 5/6 exhibited patchy immunostaining. ER was uniformly negative, and BAP1 was retained. L1CAM showed variable expression patterns. CONCLUSIONS: UATs can be reliably distinguished from their histological mimickers using calretinin or D2-40 immunohistochemistry. Positive expression of L1CAM and absence of BAP1 loss and ER expression add to the limited existing literature on the immunophenotypic profile of these rare tumors providing preliminary insights into their biology. Larger, multicenter studies are needed to validate their therapeutic implications.