Abstract Ultraviolet radiation (UVR) increases the incidence of cutaneous melanoma 1–4 . The ageing, sun-exposed dermis accumulates UVR damage 5 , and older patients develop more melanomas at UVR-exposed sites 4,6,7 . As fibroblasts are functionally heterogeneous and play key roles in the stromal contribution to cancer 8,9 , we asked whether UVR modifies dermal fibroblast function. Here we confirmed the expression of collagen-cleaving matrix metalloprotein-1 ( MMP1 ) by UVR-damaged fibroblasts was persistently upregulated to reduce local levels of collagen 1 ( COL1A1 ), and found dermal COL1A1 degradation by MMP1 decreased melanoma invasion. Conversely, we show inhibiting extracellular matrix degradation and MMP1 expression restored melanoma invasion to UVR damaged dermis. We confirmed in vitro findings in a cohort of primary cutaneous melanomas of aged humans, showing more cancer cells invade as single cells at the invasive front of melanomas expressing and depositing more collagen. We found collagen and single melanoma cell invasion are robust predictors of poor melanoma-specific survival. These data indicate melanomas arising over UVR-damaged, collagen-poor skin of the elderly are less invasive, and this reduced invasion improves survival. Consequently, although UVR increases tumour incidence, it delays primary melanoma invasion by degrading collagen. However, we show melanoma-associated fibroblasts can restore invasion in low-collagen primary tumours by increasing collagen synthesis. Finally, we demonstrate high COL1A1 gene expression is a biomarker of poor outcome across a broad range of primary cancers.

Ultraviolet light-induced collagen degradation inhibits melanoma invasion