Patients with germline mutations in CYLD can develop hundreds of benign skin tumours called cylindromas. The development of multiple tumours within a single patient at sun-protected and sun-exposed sites, varying tumour histological patterns and grades of malignancy allow for the testing of several genetic hypothesis in relation to cutaneous carcinogenesis. By adopting the unprecedented approach of whole genome sequencing of multiple benign skin tumours within individuals in multigenerational families, we set out to study the impact of mutational diversity on models such as multistep carcinogenesis as well as non-sequential carcinogenesis. Using non-negative matrix factorisation (NMF) to discover mutational signatures, we found distinct mutational signatures in identical benign tumours (N=2 patients; n=11 tumours) at sun exposed and sun protected skin tumours within a mother and her daughter. We found recurrent mutations in epigenetic modifying genes in CCS tumours which are known to have an oncogenic dependency on Wnt signalling. We also demonstrate that cutaneous tumours that metastasize to the lung carry a a UV signature, supporting the origin from the skin. Distinct malignant tumours, such as BCC and malignant spiradenocarcinoma carried unique driver mutations. These findings add new dimensions to the existing paradigms of UV-induced skin cancer and highlight the utility of studying rare disease to gain novel insights into genetic mechanisms of tumour formation.