The expression of terminal deoxynucleotidyl transferase and paired box gene 5 in Merkel cell carcinomas and its relation to the presence of Merkel cell polyomavirus DNA

Background: Merkel cell carcinoma (MCC) tumor samples frequently express B-lymphoid lineage markers. However, the reasons for expression of specific B-lymphoid lineage markers are still unclear. We studied the expression of TdT and PAX5 (two B-cell lymphoid lineage markers) in a large pool of MCC tissue microarray samples.

Methods: Immunoexpression and staining intensities of TdT and Pax-5 were statistically correlated with patient, tumor, Merkel cell polyomavirus (MCV), and disease-specific parameters.

Results: In a cohort of 117 MCC patients and their corresponding tumor samples, TdT was expressed in 37 (31.6%) samples and PAX5 in 26 (22.2%). Simultaneous immunostaining for TdT and PAX5 was observed in 13 (11.1%) samples. A statistically significant relationship was observed between MCV virus copy number and positive TdT expression (P = 0.0056). Similarly, a significant relationship was also observed between positive TdT and tumor MCV virus positivity (P = 0.000495).

Conclusion: We observed frequent TdT and PAX5 immunoexpression in MCC tumor samples. However, simultaneous immunoexpression of these markers was scarce. TdT expression was statistically significantly associated with MCV positivity. The absence of a statistically significant association between tumor parameters and disease progression markers undermines the systemic use of these markers in clinical practice.