Papillomavirus, illustration. Papillomaviruses are associated with epithelial growths and tumours. Their outer shell (capsid) is assembled from 72 pentamers of the protein L1 (dark pink) and the less common L2 protein (light pink). The capsid is geometrically regular with icosahedral symmetry. Most Human Papillomaviruses (HPV) cause no symptoms but in some people, an HPV infection can lead to warts or precancerous lesions which can increase the risk of cancer of the cervix, vulva, vagina, penis, anus, mouth, or throat.