Diagnostic Biopsy Does Not Commonly Induce Intratumoral CD8 T Cell Infiltration in Merkel Cell Carcinoma

Background: Merkel cell carcinoma is a polyomavirus-associated cancer that is strongly linked with T lymphocyte immune suppression in epidemiologic studies. CD8+ T cell infiltration into MCC tumors (intratumoral) has recently been shown to be strongly predictive of improved survival. In contrast, the presence of CD8+ T cells at the border of the tumor (peritumoral) had no independent prognostic value. Spontaneous regression has been reported for MCC approximately one thousand times more often than would be expected given the frequency of this cancer. Many of these events began shortly after biopsy, and in some cases lymphocytic infiltration was described. Methodology/Principal Findings: To determine whether CD8+ lymphocyte infiltration in MCC tumors is commonly altered by biopsy. 33 MCC patients who had microscopic confirmation of MCC on both an initial biopsy and a re-excision specimen were included in this study. Intratumoral and peritumoral CD8 lymphocyte infiltration was quantitated using immunohistochemistry and compared using the paired t-test in biopsy versus re-excision samples. There was a trend toward increased CD8 infiltration after biopsy in a peritumoral ('stalled') pattern (p = 0.08), however, biopsy was not associated with a significant increase in CD8 T cells in the clinically more important intratumoral location (p = 0.58). Conclusions/Significance: The initial diagnostic biopsy for MCC does not commonly alter intratumoral CD8+ T cell infiltration, suggesting it does not directly induce immunologic recognition of this cancer. Because CD8 infiltration is typically stable after biopsy, this parameter may be useful to assess the efficacy of future immune therapies for this virus-associated, immunogenic, often-lethal cancer.