Adenocarcinoma arising in extragonadal endometriosis: an immunohistochemical study

Malignant transformation is an infrequent but reported complication of endometriosis. Previous reports of these cases have been limited to clinicopathologic studies based on routine histologic examination of these tumors, whereas, to the authors' knowledge, characterization of these lesions based on immunophenotype and hormone receptor and oncoprotein expression has not been described.

Using commercially available monoclonal antibodies, the authors studied three recent cases of adenocarcinoma arising in extragonadal endometriosis using paraffin immunohistochemistry. Proteins examined included different cytokeratin (CK) subtypes, as well as hormone receptor status, proliferation rate, and oncoprotein expression.

All three cases presented clinically and macroscopically as colonic masses, and the tumors expressed an endometrial CK phenotype (CK7+, CK20-). In contrast, the adjacent benign colonic epithelium expressed the expected opposite phenotype (CK7-, CK20+). Estrogen receptor (ER) and progesterone receptor (PR) were expressed in one of the three tumors. Interestingly, in the ER/PR negative tumors, receptor expression was present in areas of benign endometriosis adjacent to malignancy, suggesting a loss of receptor expression with malignant transformation. The tumors also were examined for proliferation by Ki-67, and the expression of oncoproteins c-erb B-2, p53, cyclin D1, and bcl-2. All cases of malignancy had a high proliferation rate as measured by Ki-67, which was in contrast to areas of benign endometriosis which had a low proliferation rate. Of the other oncoproteins only p53 protein was detected at a significant level in all three cases. Cyclin D1 was overexpressed in two of the three cases. c-erb B2 and bcl-2 overexpression was not detected.

The results of the current study 1) show the utility of CK subtypes in confirming endometrioid phenotype in tumors arising in extragonadal endometriosis with colonic involvement and 2) suggest that loss of hormone receptor expression and p53 oncoprotein abnormalities may be involved as mechanisms in malignant transformation in extragonadal endometriosis.