Endometrioid tubal intraepithelial neoplasia (E-TIN): case report & literature review

An endometrioid carcinogenic pathway of the fallopian tube with possible potential precursors including type II SCOUTs (secretory cell outgrowths) and E-TIN (endometrioid tubal intraepithelial neoplasia) has been recently documented. We report an incidental focus of E-TIN identified in a hysterectomy specimen for Grade 1 endometrioid type endometrial carcinoma. The lesion was present at the fimbriated end of left fallopian tube involving 1 plica. It comprised crowded glandular proliferation with a pseudostratified columnar lining. The cells displayed elongated nuclei with no remarkable nuclear atypia.Immunohistochemistry showed patchy loss of PAX 2 expression with multifocal aberrant nuclear and cytoplasmic staining for B-catenin. p53 was wild-type and ER was positive.In view of the co-existing endometrioid type endometrial carcinoma, a possible metastatic spread to the fallopian tube was considered. However, morphologically no obvious nuclear atypia noted, and no associated inflammatory response or desmoplastic stromal reaction identified within the tubal lesion. And on immunostaining, the endometrial tumour was distinct from the tubal lesion. For instance, PTEN was negative/lost in the endometrial tumour but retained in the tubal lesion and B-catenin was membranous in the endometrial tumour but aberrant with multifocal nuclear and cytoplasmic overexpression in the tubal lesion. WT1 was negative in the endometrial tumour but positively expressed by the tubal lesion. All the above findings favoured the possibility of the tubal lesion as being independent of the endometrial primary. In conclusion, we describe an incidental B-catenin aberrant endometrioid type proliferation of the fallopian tube/E-TIN, to raise awareness of such lesions.