P504S/alpha-methylacyl-CoA racemase, HNF1β and napsin A in morular metaplasia and clear cell carcinoma of the endometrium: An immunohistochemical analysis.

AIMS: Endometrial morular metaplasia (MorM) can show cytoplasm clarification, which may mimic clear cell carcinoma (CCC), especially on biopsy. We aimed to assess the expression of CCC markers in MorM.

METHODS

Twenty cases of MorM with areas of cytoplasmic clarification were assessed by immunohistochemistry for HNF1β, Napsin A, and P504S/alpha-Methylacyl-CoA racemase (AMACR); 60 tumors were selected as controls (20 classical MorM, 20 conventional squamous differentiation and 20 CCC).

RESULTS

Eighteen cases (90%) showed overt squamous/keratinizing areas within MorM, and 11 cases (55%) showed isolated ghost cells which might mimic the hyaline globules of CCC. All cases (100%) showed expression of AMACR, which was mostly diffuse and strong; in all cases, the expression was restricted to the prototypical MorM areas, while glandular areas and overtly squamous areas were negative. Twelve cases (60%) showed HNF1β expression, which was focal/multifocal and/or weak; the expression was found in all tumor components. No case showed Napsin A expression in any component. Classical MorM showed similar immunophenotype, while conventional squamous differentiation did not show AMACR expression. Most CCC expressed AMACR (70%), HNF1β (85%), and Napsin A (75%), mostly with diffuse and strong positivity.

CONCLUSION

MorM may show features that mimic CCC and consistently expresses AMACR, which may be accompanied by HNF1β expression; Napsin A is consistently negative instead. These findings should be considered to avoid overdiagnosis.