De Martino, Ciro, et al. “Squamous-Cell Carcinoma and Pilonidal Sinus Disease. Case Report and Review of Literature”. Annali Italiani Di Chirurgia, vol. 82, no. 6, Nov. 2011, pp. 511-4, https://annaliitalianidichirurgia.it/index.php/aic/article/view/3088.