Defining the molecular landscape of cancer-associated stroma in cutaneous squamous cell carcinoma. Defining the molecular landscape of cancer-associated stroma in cutaneous squamous cell carcinoma

Cutaneous squamous cell carcinoma (cSCC) is the 2nd most common skin cancer world-wide. Cancer-associated stroma (CAS) plays a central role in initiation and progression of cancer and strongly influences therapy response. Perineural infiltration (PNI) represents a major risk factor for cSCC and is likely to influence CAS reprogramming. However, stromal reprogramming in cSCC remains poorly characterized, and it is unknown whether and how PNI influences CAS. To gain insight into CAS in cSCC and investigate the influence of PNI on stromal reprogramming, we analyzed CAS and matched normal stroma isolated from 15 cases (4 with and 11 without PNI) of cSCC by laser-capture microdissection using RNA sequencing. Our analysis reveals massive stromal reprogramming in cSCC that is strongly driven by changes in immune cell populations, as validated using immunohistochemistry. Furthermore, CAS of cSCC displays markers of immune exhaustion including PD-1, CTLA-4, HAVCR2, TIGIT and LAG3. Finally, we demonstrate that PNI strongly influences CAS and leads to increased IL-17 signaling and immunosuppression therein. In conclusion, our detailed analysis elucidates the molecular landscape of stromal reprogramming in cSCC and identifies the presence of immunosuppressive mechanisms in CAS which support the use of immunotherapies in cSCC especially for therapy of cases with PNI.