Microsatellite instability in penile cancer: comparative analysis of primary tumors and metastases.

Background: Penile cancer (PeCA) presents high morbidity and mortality and is more prevalent in underdeveloped countries. The presence of nodal metastasis at diagnosis or as early recurrence carries a worse prognosis, making it important to determine whether clinically relevant biomarkers are maintained between primary tumors and corresponding lymph node metastases. We aim to describe the presence of DNA microsatellite instability (MSI) in primary PeCA tumors and locoregional lymph nodes affected by metastatic cells, as well as to assess HPV status through p16 expression. Methods: A total of 116 patients were comparatively evaluated between the primary tumor and lymph node metastases. The evaluation of p16 and mismatch repair proteins was done by immunohistochemistry, and MSI status was assessed using a hexa-plex marker by polymerase chain reaction, followed by fragment analysis. Results: All patients underwent a standard lymphadenectomy (inguinal or pelvic), with a pN0 frequency of 33.6%. MSI-H was found in three patients (2.6%), with correspondence between the presence of the biomarker in the primary tumors and the lymph node metastases. A second validation was performed using IHC for MMR, with MLH1/PMS2 loss in MSI-H cases. 22.8% of patients expressed p16 by immunohistochemistry. p16 positivity was associated with a 55% reduction in the risk of death. All MSI-H patients were p16 positive. Conclusion: MSI-H occurs in 2,6% of the sample and is associated predominantly with MLH1/PMS2 loss and p16 positivity. Together, these findings suggest potential interactions between HPV- associated carcinogenesis and genomic instability. Further prospective, biomarker-driven trials are warranted to define their prognostic and therapeutic relevance in PeCA.