Background Vulvar squamous cell carcinoma (VSCC) is an aggressive and highly mutilating disease. It arises through the malignant transformation of healthy vulvar tissue to invasive carcinoma, via an HPV infection or a P53 or other mutation dependent manner. Currently all molecular subgroups receive the same treatment type, consisting of surgery and/or (chemo)radiation, with limited success and high morbidity. In-depth information on the immunological make up of VSCC is pivotal in order to assess if immunotherapy may form a potent alternative treatment.

Methods A total of 104 different patient samples comprising healthy vulva (n=27) and VSCC (n=77) were immunologically dissected. Multispectral immunofluorescence (15 markers, in situ high-resolution single-cell proteomics) was used to study both the myeloid and lymphoid immune cell composition. Transcriptomic differences were studied with Nanostring nCounter (1258 genes). The impact of the immune composition on survival was analyzed by Kaplan Meier curves.

Results The transformation of healthy vulva into cancer is associated with an increase in stroma infiltrating myeloid cells and epithelium infiltrating lymphoid cells. In contrast to the lymphoid cell infiltrate, the density and composition of the myeloid cell infiltrate strongly differed per molecular subgroup of VSCC. Two myeloid cell phenotypes were identified to be strong predictors for improved survival, independent of T cell infiltration, disease stage or molecular subgroup: epithelial monocytes and stromal dendritic cells. The presence of epithelial monocytes was associated with the increased expression of stem-cell like features by the tumor. Survival analyses revealed that a strong infiltration with T cells and/or the identified epithelial monocytes was associated with drastic superior survival: 5-year survival >90% when either one is high, versus 40% when both are low (p-value<0.001).

Conclusions In conclusion, a hot myeloid and/or lymphoid infiltrate predicts excellent survival in VSCC patients. Patients with either a hot myeloid or lymphoid VSCC infiltrate are likely to respond well to neoadjuvant immunotherapy. Based on these findings a clinical trial exploring the potential of neoadjuvant checkpoint blockade in VSCC has opened.