Plasmacytoid dendritic cells and M2 macrophages are associated with clinical outcomes in human papillomavirus–independent vulvar squamous cell carcinoma

Background Vulvar squamous cell carcinoma (VSCC) is a rare malignancy comprising HPV-associated (HPV-A) and HPV-independent (HPV-I) subtypes. HPV-I is associated with high recurrence rates and poor survival, yet lacks validated prognostic biomarkers and therapeutic stratification tools. Although immunotherapy has transformed cancer care and highlighted the tumor microenvironment (TME) as an important determinant of clinical outcome, the rarity of VSCC has limited its molecular characterization, and the TME remains poorly understood. We therefore aimed to define the VSCC TME in an HPV-specific context and identify immune features associated with clinical outcomes. Methods We analyzed 70 surgically treated VSCC (18 HPV-A and 52 HPV-I) using targeted transcriptomic profiling (HTG EdgeSeq). Immune and stromal cell composition was inferred by computational deconvolution, primarily with xCell and supported by EPIC, quanTIseq and MCPcounter. TME composition was compared by HPV status and, within HPV-I VSCC, by p53 and PD-L1 immunohistochemical status. Associations with recurrence-free and disease-specific survival were assessed using Firth-penalized Cox regression adjusted for FIGO stage and p53 status, and candidate populations were evaluated by CD123 and CD163 immunohistochemistry. Results HPV-A tumors showed higher immune and overall microenvironment scores, with enrichment of diverse lymphoid and myeloid populations, whereas HPV-I tumors showed lower immune-cell enrichment. Within HPV-I VSCC, plasmacytoid dendritic cell (pDC) enrichment showed the most consistent association with favorable survival across deconvolution-based analyses, with immunohistochemistry confirming CD123 + cell infiltration as an independent favorable prognostic factor. PD-L1 positivity occurred in 44% of HPV-I tumors and was associated with CD163 + macrophage infiltration, which, in turn, was independently associated with poor outcomes. Conclusions TME profiling identified two clinically relevant immune populations within HPV-I VSCC: CD123 + cell infiltration was associated with favorable outcomes, whereas CD163 + macrophage infiltration was associated with PD-L1 positivity and poorer outcomes. These findings provide a rationale for further investigation of the TME as a source of prognostic and potentially therapeutic biomarkers. Validation in larger, independent cohorts is required before clinical utility can be established.