The Role of Plasmacytoid Dendritic Cells in the Immune Contexture of TP53-Mutated High-Grade Serous Ovarian Cancer

Background/Objectives: This study aimed to characterize dendritic cell (DC) heterogeneity, immune associations, and prognostic relevance across three TP53-mutated tumor entities—high-grade serous ovarian cancer (HGSOC), triple-negative breast cancer, and endometrial cancer—focusing on plasmacytoid DCs (pDCs) in HGSOC. Methods: RNA-sequencing and clinical data of 603 patients from The Cancer Genome Atlas were analyzed. DC subset abundance was assessed for cDC progenitor, conventional DC type 1 (cDC1), conventional DC type 2 (cDC2), plasmacytoid DC (pDC), and mature DC by marker gene signatures. Differences in DC scores across tumors were analyzed using Kruskal–Wallis. Survival analyses were performed using Kaplan–Meier and Cox regression. Spearman’s correlation was used to determine associations between parameters. Results: HGSOC showed the lowest pDC abundance, yet high pDC scores were independently associated with shorter PFS (HR = 1.55, 95% CI: 1.05–2.27; p = 0.027), representing the only DC-subset-related prognostic signal observed across tumor types. pDCs correlated positively with neutrophils and negatively with monocytes, and pDCs, cDC2s, and cDC progenitors correlated inversely with TMB. No consistent link was found between pDC and TP53 mutation classes. However, tumors harboring specific TP53 mutations within established hotspot regions exhibited significantly lower pDC levels (p = 0.015). Conclusions: Our findings reveal distinct DC infiltration patterns and highlight the immunological vulnerability of TP53-mutated HGSOC. pDCs appear to exert a tumor-promoting, immune-evasive role, suggesting that DC function depends on their programming and tumor context. Selective targeting of DC subsets may offer novel therapeutic opportunities in TP53-mutated, low-TMB cancers.