Invasive stratified mucin-producing carcinoma of the cervix: a report of 34 cases of immunohistochemical and clinicopathological findings.

Objectives: This retrospective study aims to explore the immunohistochemical profile and clinicopathological features of invasive stratified mucin-producing carcinoma (ISMC). Methods: A total of 34 cases of ISMC were selected for this study. ISMCs are classified as either pure or mixed subtype, based on whether they are combined with tumor cells of other pathological types. We compared the clinicopathological features of ISMC with those of human papillomavirus (HPV)-associated cervical endocervical adenocarcinoma, as well as the differences between pure and mixed ISMC, through retrospective analyses. Results: Approximately 47% (16 out of 34) of the ISMC cases were classified as pure ISMC. There was no significant difference in clinicopathological features between pure ISMC and mixed ISMC. When compared to HPV-associated endocervical adenocarcinoma, ISMC cases presented with an earlier age of onset, larger tumor size, more aggressive biological behavior, and poorer prognosis. All cases exhibited block positivity for p16, positivity for CK7, and a higher Ki-67 labeling index. The expressions of CK5/6, Pax-8, P40, and P63 at the peripheral and mesenchymal junctions of the cancer foci were focally positive. Periodic acid-Schiff (PAS) staining demonstrated intra- and extracellular mucus in the cytoplasm of the tumor cells. Conclusion: The proportion of mixed ISMC cases is similar to that of pure ISMC. ISMC is more aggressive compared to HPV-associated endocervical adenocarcinoma and is associated with shorter progression-free survival. We recommend the following markers as a diagnostic panel for ISMC: p16, CK7, CK5/6, P40, P63, Pax-8, and PAS.